In France, gâteau au yaourt is a cake that comes together so easily it’s often the first recipe children are taught. It has a fine, moist crumb similar to a pound cake, but isn’t nearly as rich. We boost the flavor by adding grated citrus zest and fragrant spice to the batter. Citrus juice whisked with powdered sugar makes a quick finishing glaze, though the cake is equally good unadorned. Feel free to use whatever kind of citrus you have on hand—lemon, lime, orange or even grapefruit. The cake will keep for up to three days, tightly wrapped and stored at room temperature.