Combine flour, sugar, butter, cornstarch, cinnamon, baking powder, and salt with your hands or a fork until a soft crumble forms. Set aside.
1 1/4 cups all-purpose flour, 1/4 tsp baking powder, 1/2 cup white sugar, 7 tbsp unsalted butter, 1 tsp cornstarch, 1/4 tsp salt, 1/4 tsp cinnamon