What makes a dessert a good keeper?
You can tell if a cake will keep well at room temperature just by reading the recipe. If it includes a good amount of butter or oil, along with brown sugar, liquid sweeteners like honey, molasses, or jam, or fruit and vegetable purées, it’s a keeper. These hygroscopic ingredients absorb moisture from the environment. That’s why a cake made with pumpkin, brown sugar, and butter tastes richer and more flavorful when given a day or two to rest before serving.
Desserts that freeze and defrost well are also good keepers. Not every dessert freezes well—sponge cakes dry out and custard pies can get watery when defrosted. But moist, dense, intensely flavored cakes are great candidates. (Note that it’s best to freeze cakes without frosting them, since freezing will compromise the texture of a glaze or ganache. Fortunately, both are easy to stir together later.)
Because they are loaded with fat or sugar or both, buttery shortbread desserts and syrupy nut-filled pies freeze and defrost beautifully. Unlike custard and cream pies, they have little liquid, so when they freeze, fewer ice crystals form; it’s the thawing ice crystals that can change the texture of a pie and make the crust soggy. These tarts need only a little reheating in the oven to crisp up the crust for a just-baked texture and flavor.