In a large bowl, combine the flour, brown sugar, baking powder, salt and baking soda. Cut in 1/2 cup butter until mixture resembles coarse crumbs. Combine pumpkin and buttermilk; stir into crumb mixture just until moistened.

Turn onto a lightly floured surface; knead 8-10 times. Pat or roll out to 1-in. thickness; cut with a floured 2-1/2-in. biscuit cutter–the top of a mason jar works great. Place 1 in. apart on a greased baking sheet.
Bake at 425° for 18-22 minutes or until golden brown. Brush butter over biscuits. Serve warm.