Easy Gluten Free Rhubarb Bars

These gluten-free rhubarb bars bring together a rich, buttery oat crust with a luscious rhubarb and raspberry jammy filling. Made with oat flour and certified gluten-free oats, they’re an excellent choice if you’re steering clear of gluten but still want big flavor and that perfect chewy texture. The method is easy: cook down the fruit into a thick compote with cornstarch or tapioca, prebake a quick oat crust, layer it all up, then bake again until golden and irresistible.

They hold up well in the fridge and freeze beautifully, which makes them a go-to dessert for springtime get-togethers, brunches, or whenever you want a make-ahead sweet treat. For serving, these bars shine cold alongside a scoop of vanilla ice cream or a sprinkle of powdered sugar for a little extra charm.

When rhubarb’s tartness meets the sweetness of juicy raspberries, magic happens in these gluten-free bars that feel both special and seasonal—but without any fuss. The foundation is a tender oat shortbread crust crafted from oat flour and gluten-free oats, while the fruit filling is a thickened compote that sets up snugly between the crust and a crisp oat topping.

This recipe is easy to follow: simmer the fruit down to jammy perfection, prebake a simple oat crust, spread on that vibrant compote, then finish with the rest of the oat topping and bake until golden brown. It calls for familiar pantry staples, offers easy ingredient swaps if you need them, and results in bars with a nicely set filling and a gently firm, chill-worthy texture.

• Flavor: a bright, tangy punch from rhubarb balanced perfectly with sweet raspberries and rich brown sugar.
• Texture: flaky buttery oat crust, luscious jammy filling, and a crisp top layer.
• Time & skill: roughly 55 to 75 minutes total; skill level: medium.
• Make-ahead friendly: these bars keep well in the fridge for days and freeze for several months without losing their charm.

Keep reading for detailed ingredient amounts, simple step-by-step instructions, plus insider tips to nail that silky compote and tender oat crust every time.

Why You’ll Love Them

• Gluten-free friendly – Crafted from oat flour and certified gluten-free oats, these bars satisfy your gluten-free diet without skimping on flavor or texture.
• Make-ahead friendly – You can use fresh or frozen fruit (like frozen rhubarb), so these bars work all year round and keep nicely for days in the fridge.
• Simple ingredients – No need to hunt for fancy items; this recipe sticks to pantry staples paired with fresh seasonal fruit—much like this easy rhubarb dump cake.
• Perfect balance of flavors – Tart rhubarb pairs beautifully with sweet raspberries and brown sugar, while the oat crust gives a wonderful contrast in texture.

What You’ll Need

• zest and juice of 1 lemon (freshly zested and squeezed for the brightest flavor)
• 1/2 tsp vanilla extract
• 1/3 cup plus 1 tbsp cane sugar
• 2 cups chopped rhubarb (fresh or frozen and fully thawed)
• 3 tsp cornstarch (I trust Argo 100% Pure Corn Starch for thickening)
• 1 1/4 cups raspberries
• 1/2 cup packed brown sugar
• 1 cup oat flour
• 3/4 cup old-fashioned oats (make sure they’re certified gluten-free)
• 1 tbsp tapioca starch (helps thicken and bind the bars)
• 1/4 tsp sea salt
• 1 1/4 tsp baking powder
• 1/4 tsp ground cinnamon
• 1/2 cup melted vegetable shortening (I like Crisco, but butter works great too)

Step-by-Step Method

1. Combine chopped rhubarb, raspberries, cane sugar, lemon zest and lemon juice in a saucepan over medium heat.
2. Bring the fruit mixture to a strong boil, stirring frequently to prevent burning.
3. Simmer about 10 minutes until the fruit breaks down and becomes jammy.

4. Sprinkle in cornstarch or tapioca starch and stir until fully dissolved.

   

5. Simmer 3 more minutes to thicken the compote.
6. Stir in vanilla, remove the pan from heat, and let the filling cool about 15 minutes.
7. Preheat oven to 350°F (175°C).

8. Whisk together oat flour, gluten-free oats, packed brown sugar, tapioca starch, baking powder, sea salt, and cinnamon in a large bowl.

   

9. Add melted shortening or butter and stir until the mixture is evenly moist without white streaks.
10. Line an 8×8-inch baking pan with parchment paper.
11. Press about a heaping cup of the oat mixture firmly into the bottom of the pan using the back of a spatula or spoon.

12. Prick the crust several times with a fork.

    

13. Bake the crust for approximately 12 minutes until lightly golden and fragrant.
14. Remove the crust from the oven and cool about 10 minutes.
15. Spread 1 1/4 cups of the cooled rhubarb compote evenly over the crust.

16. Sprinkle the remaining oat mixture evenly over the compote.

    

17. Bake 25 to 30 minutes more until the topping is golden brown.
18. Remove the pan and cool completely to room temperature.
19. Chill the bars in the refrigerator until firm.

20. Cut the chilled bars into squares.

    

Expert Tips for Success

The key to these gluten-free rhubarb bars is getting your oat crust just right. Be careful not to over-mix when combining the dry ingredients and melted fat—that can make the crust tough or overly dense. When cooking the fruit, don’t skip the cornstarch or tapioca starch; these thickeners help the filling set instead of running everywhere. Keep an eye on baking time too—bars can shift from golden perfection to overdone fast, so start checking about 5 minutes before your timer goes off. Lastly, patience pays off: let your bars cool completely before slicing to prevent crumbly, falling-apart squares.

These bright, tart bars are perfect for afternoon tea or a casual dessert, and they pair beautifully with a few simple sides. For a tea-time spread, consider adding Rhubarb Greek Yogurt Muffins alongside. A scoop of vanilla ice cream or a dollop of whipped cream adds a refreshing richness that balances the tang of the fruit. For a cozy treat, serve alongside your favorite cup of tea—I’m partial to Earl Grey—or fresh brewed coffee. Hosting friends? Try arranging the bars with fresh berries or a light sprinkle of powdered sugar for an easy but elegant touch.

Easy Swaps and Add-Ins

• Berry swaps: Swap out raspberries for strawberries or blackberries. Strawberries lend a sweeter, familiar strawberry-rhubarb flavor, while blackberries add a deeper, earthy berry flavor.
• Flour alternatives: Almond flour or a gluten-free all-purpose blend can replace oat flour. Expect a slightly softer texture but a delicious outcome all the same.
• Fat and vegan options: Use melted butter, coconut oil, or a dairy-free butter substitute instead of vegetable shortening to make these bars vegan or just shift up the flavor.
• Thickener swaps: Arrowroot powder works perfectly instead of cornstarch or tapioca starch if you prefer.
• Sweetener swaps: Regular granulated sugar is a fine substitute for raw cane sugar, or try coconut sugar for a touch of caramel flavor—just note it will darken the bars slightly.
• Add-ins: Mix in 1/2 cup toasted chopped nuts like pecans or almonds, or 1/3 cup shredded coconut for texture. You can also sprinkle a handful of oats on top for a rustic look and crunch.
• Spice and citrus twists: Add a pinch of ground ginger or cardamom to the crust for extra warmth, or ramp up the lemon zest in the filling for a brighter, zestier punch.
• Format changes: Bake in a larger pan for thinner bars, crumble the topping for a streusel effect, or spoon the compote into oat-lined muffin tins for portable mini treats—see Rhubarb Muffins with Yogurt for timing cues.

Storing and Freezing Tips

Keep Fresh: Store these rhubarb bars in an airtight container in the fridge for up to five days. I like to separate layers with parchment paper so they don’t stick together. Honestly, they taste even better the next day when the flavors have had a little time to meld!

Freeze: If you want to stash some away, cut the bars into squares and layer them in a freezer-safe container with parchment paper between each layer. Freeze for up to three months. When you need a quick gluten-free treat, just thaw and enjoy!

Thaw: To thaw frozen bars, simply transfer them to the fridge overnight or let them sit out at room temperature for about 30 minutes. The texture stays pretty great, though the top might be slightly less crisp than fresh-baked.

Preparation Time 15-30 minutes Cooking Time 40-45 minutes Total Time 55-75 minutes Level of Difficulty Medium

Common Questions Answered

You can absolutely use fresh or frozen rhubarb for these bars (or in a cozy bake like Warm Rhubarb Cake with Butter Sauce), so no stress if fresh stalks aren’t in season or available at your market. When picking fresh rhubarb, look for crisp, firm stalks with a bright pink to deep red color—though color doesn’t actually change the taste much. Aim for stalks about 10 to 15 inches long and skip any that are floppy or have blemishes. If you’re using frozen rhubarb, no need to thaw it first—just toss it straight into your compote and adjust cooking time slightly if necessary.

• Oats and oat flour: Always use certified gluten-free oats. If you like, make your own oat flour by blitzing gluten-free oats in a food processor until fine. Almond flour or gluten-free all-purpose blend can also work as substitutes—they just change the texture a little.
• Tapioca/cornstarch: Either works perfectly to thicken your compote and bind the bars. Arrowroot powder is also a great option to swap in equally.
• Vegetable shortening: You can swap for melted butter, coconut oil, or dairy-free butter substitutes. Just be sure it’s fully melted when adding.
• Raspberries: If raspberries aren’t your jam, swap in strawberries or blackberries. Each offers a unique but yummy flavor twist.
• Raw cane sugar: Regular granulated sugar is a simple swap, or try coconut sugar for a caramel note—though that will darken the bars a bit.
• Rhubarb: Essential for authentic rhubarb bars! In a pinch, tart apples are a backup, but they’ll change the classic flavor and texture. Got extra stalks? A quick rhubarb applesauce is a great way to use them up.