Buttermilk: Substitute 1 cup plain yogurt or 1 tablespoon lemon juice stirred into 1-cup milk; let stand 5 minutes. Sour cream: Substitute 3 tablespoons melted butter stirred into buttermilk or yogurt to make 1 cup. Whole milk: Substitute equal ports evaporated milk and water or 2 teaspoons butter plus 1 cup skim milk (or water). Sour milk: Substitute 1 cup buttermilk or 1 tablespoon lemon juice stirred into 1 cup milk; let stand 5 minutes. Heavy (whipping) cream: Substitute 1/3 cup melted butter plus 3/4 cup milk. Ricotta cheese: Substitute cottage cheese, drained of liquid. tips 6