6 to 7 tablespoons unsalted butter
1 cup all-purpose flour
1/2 cup sugar
1/2 teaspoon ground cinnamon
1/4 teaspoon baking powder
1/4 teaspoon salt
Place the butter in a 2-quart heavy-bottomed saucepan and heat until almost melted; remove from heat and cool to tepid.
Whisk together the flour, sugar, cinnamon, baking powder, and salt. Add to the butter and stir with a fork until blended and mixture begins to form crumbs. Gently squeeze the mixture with your hand to form larger clumps, then break them apart with your fingers. Before using, let the streusel stand for 10 to 15 minutes.