Combine 1/2 cup all-purpose flour, 1/2 cup brown sugar, and 1/4 teaspoon salt
Add 1/4 cup cold unsalted butter, cut into small pieces
Mix with a fork or your fingers until crumbly
Add 1/2 teaspoon ground cinnamon if desired
Stir in 1/4 cup chopped nuts or oats if desired
Sprinkle over muffins, cakes, pies, or coffee cake before baking
Bake until golden and crisp