Use fresh rhubarb stalks that are firm and bright pink or red for best flavor; avoid limp or spotty stalks., When using frozen rhubarb, thorough thawing and drying is essential to avoid soggy cake., Tossing frozen rhubarb with a tablespoon of flour before adding to batter helps control moisture., Avoid overmixing the batter to prevent dense or chewy cake texture., Butter sauce should be cooked slowly over medium-low heat and whisked constantly to prevent graininess or separation., The cake can be baked a day ahead and stored at room temperature covered., Butter sauce can be made up to three days in advance and stored refrigerated; reheat gently before serving., Cake stores well at room temperature for 2 days, butter sauce refrigerated for 3-5 days, and cake freezes up to 3 months (without sauce)., Serve with vanilla ice cream, whipped cream, or fresh berries like strawberries for added indulgence., Substitutions: Use 2% or plant-based milk for lighter cake; half-and-half for a lighter sauce; cake flour for lighter texture; vegetable oil instead of melted butter in cake batter (sauce butter should not be substituted)., Alternative fillings: tart apples (add lemon juice to maintain tartness), cranberries, or strawberries can be used instead of rhubarb.