Churn the flour, sugar, baking powder, and salt in a food processor fitted with the metal chopping blade a couple of seconds until well blended. Tap half the mixture onto a large piece of waxed paper and reserve.
Scatter half the butter evenly over the dry ingredients in the processor and pulse 6 to 8 times. Pulse quickly 3 to 5 times more until the mixture is about the texture of lentils. Empty the mixture into a large mixing bowl.
Return the reserved dry mixture to the food processor, scatter the remaining butter evenly on top, and cut in as before. Add to the mixture in the bowl.
Toss the 2 batches together well, then spoon into a large zipper freezer bag, press out the air, and seal. Label, date and store in the freezer. This quick cake mix will last at least 2 months in the freezer, 1 week to 10 days in the refrigerator.
Scoop out the frozen mix ¿ no need to thaw ¿ and use as individual recipes direct.
Recipe courtesy Jean Anderson, Quick Loaves, HarperCollins, 2005