Mayonnaise adds a moist texture and rich flavor to baked goods, and it's a worthy substitute when you're out of eggs. The substitution formula is simple, but measure accurately to produce the delicious effect that you want.
Read the baking recipe. If it calls for eggs and a fat, such as butter or oil, you know you can substitute mayonnaise.
Calculate the total amount of eggs and fat called for in the recipe. It is customary to use large eggs when baking, unless the recipe indicates otherwise; one large egg is equivalent to 2 tablespoons of mayonnaise. Two eggs equals 4 tablespoons, or 1/4 cup of mayo.
Measure the same amount of mayonnaise as the recipe calls for in fat and eggs. For example, if your cake recipe lists two eggs and 1/2 cup of canola oil, use 3/4 cup of mayonnaise instead.