Pastry cream is a foundational recipe in French dessert making. It's used on its own (in éclairs and fruit tarts, for example) and is the basis for half a dozen other essential dessert creams.
Mashed potatoes are the ultimate comfort food. They're quick and easy and the soft texture makes me feel like a kid. They're also a great base for all kinds of variations like garlic mashed potatoes and herby mashed potatoes.