If using frozen lobster, thaw completely and pat dry to avoid watering down the sauce., Save a little pasta water when draining to thin sauce if it becomes too thick., Cook roux just until lightly browned for a nutty flavor without bitterness., Add cheese on low heat and stir continuously to avoid grainy sauce; high heat can ruin texture., Thin sauce with warm milk or reserved pasta water if necessary., For a crunchy topping, toss panko breadcrumbs with melted butter, sprinkle on top, and broil briefly after transferring to an oven-safe dish., Cheese substitutions: Gruyère or fontina can replace Swiss for nuttier flavor., Spice variations include cayenne pepper, smoked paprika, or Old Bay seasoning., Seafood substitutions: cooked shrimp or crab can replace lobster., Brighten flavor with lemon zest or fresh lemon juice before serving., Refrigerate leftovers in an airtight container for 3 to 4 days., Freezing is possible but not ideal; thaw overnight before reheating., Reheat gently on low heat on stove with added milk or in oven at 325°F (160°C), uncovering briefly to crisp topping.