Why your vegetable muffins might turn out dense and unevenLight, souffle-like muffins that rely on whipped eggs and minimal flour come together quickly, but the texture hinges on one non-negotiable step: the vegetable filling must be completely cold before it meets the egg mixture. If warm onions and peas hit the whipped base, the proteins set too early and the crumb turns dense and uneven. This is essential — any residual heat will prematurely coagulate the whipped eggs. If you add hot onion and peas to whipped eggs, the protein will begin to coagulate prematurely, and the muffin structure will become uneven." Yes — any neutral vegetable oil or melted butter works.