In a large bowl combine the flour, sugar, cocoa powder, baking powder and salt. Whisk to combine.
Use a pastry cutter to blend in the butter.
Store in an airtight container and refrigerate until ready to use.
Notes
Can you Substitute cake flour for all-purpose?
Yes! If using all-purpose flour instead of cake flour, you will only need only need 2 cups unbleached all-purpose flour. However the cakes crumb/texture will be different.