Leche Flan with Grapefruit

Some of the first churches in the Philippines, built of adobe, limestone, or coral, were bound together by egg whites, mixed into the mortar to make it stronger. As the food historian Pia Lim-Castillo has written, millions of eggs were likely sacrificed to the cause—and something had to be done with all those leftover yolks. Rather than let them go to waste, enterprising cooks turned them into desserts, most beloved among them leche flan.

The original recipe, for a wobbly custard wi