Preheat oven to 425 degrees.  In a large bowl, whisk together flour, baking powder, salt, and baking soda  together.

With a box grater, grate the frozen butter into the flour mixture. (I just finely chopped my frozen butter)With a pastry blender or a fork, cut in butter until mixture resembles coarse meal (I did this with my food processor), this should not take very long because the butter is already grated well.

In a liquid measuring bowl, whisk together pumpkin purée, buttermilk, and brown sugar; stir quickly into flour mixture until combined (do not over mix).

Turn out dough onto a lightly floured surface, and gently bring together, folding once or twice and adding a Tablespoon or two of flour as needed so the dough is not too wet. Shape into a disk, and pat to an even 1-inch thickness (I shaped it into a square). With a 2-inch biscuit cutter dipped in flour, cut out biscuits as close together as possible (I skipped this part and just cut the dough with a knife into 9 squares). Gather together scraps, and repeat to cut out more biscuits (do not reuse scraps more than once).

Arrange biscuits on a buttered or parchment lined baking sheet, or side by side in an 8-inch cake pan. Smear a bit of butter on the top of each biscuit. Bake until golden, rotating once, 20 to 24 minutes. Serve piping.