Flan is a dessert made with eggs, sugar, vanilla, and whole, condensed, or evaporated milk to create a creamy mixture that's baked or steamed and topped with caramel syrup.
Custard combines eggs, milk or cream, and sugar and is cooked to create a thick consistency. The eggs bind the ingredients together and give it a silky, gelatinous texture.
Pudding is thickened with starch, like cornstarch or flour, rather than eggs. While custard holds its shape, the addition of starch creates a more malleable texture.
Flan does not contain flour, so it falls in the custard category. The use of eggs makes the process delicate since high heat can scramble and ruin the eggs' texture.
Masterclass suggests using a double-boiler or water bath — a baking pan filled with hot water — to use indirect heat to steam and cook the custard dish in ramekins.
Flan is known as flan de huevo in Spain, and in countries that Spain colonized, they introduced this dessert, which eventually became a local favorite.
In Mexico, it is called flan napolitano, and in the Philippines, leche flan differs slightly, using evaporated or condensed milk rather than whole milk.