On the slopes of a volcano in central Mexico, biologist Cuauhtémoc Sáenz-Romero and his team envision a climate refuge for oyamel fir trees and the monarch butterflies that depend on them.

But with a little ingenuity, eggless cakes, biscuits, brownies and meringues can be delicious. There are many substitutes, but it’s important to use the right one for the result you want.