Quark
Quark is a versatile fresh cheese that resembles soft cream cheese. Germans (who call it quark) and Austrians (who call it topfen) use it to make everything from cheesecake to gravy.
To make your own: Combine one quart whole milk with 1/2 cup buttermilk in a clean container, cover, and let the mixture stand at room temperature for two days. Gently cook the mixture for about 30 minutes. It's done when the curd has thickened slightly and begun to separate from the whey. Let it cool and pour it into a colander lined with several folds of cheesecloth. Put the colander into a larger container, wrap with plastic, and let it drain overnight in the refrigerator until the quark is reduced to the consistency of yogurt. Makes about 1 cup.
Substitutes: fromage frais (very similar) OR yogurt cheese (more acidic) OR two parts ricotta cheese and one part sour cream OR strained cottage cheese OR mascarpone