4 tablespoons(57 grams) cold unsalted butter, cut into 1/2-inch cubes
Instructions
In a medium bowl, stir the oats, all-purpose flour, whole-wheat flour, brown sugar, baking powder, salt, and cinnamon to combine. Cut the butter into tablespoon portions and drop them into the bowl. Mix with your hands or a pastry cutter until the mixture comes together to form large clumps.
To use, crumble the streusel over the top of a pie that requires baking and bake as the recipe instructs. If the topping is browning too quickly, tent it with foil for the remainder of the bake time.