Line a 9- by 13-inch baking sheet with parchment paper. In a large bowl, whisk together the flour, baking powder, baking soda, nutmeg and salt. Using a fine-mesh sieve, sift in the brown sugar. Using your fingertips or a pastry blender, combine the butter with the dry ingredients until the mixture resembles oatmeal. Fold in the nuts. Combine the pumpkin and milk; fold into the mixture. Using a fork, stir until a soft dough forms. Drop the dough by rounded spoonfuls about one inch apart onto the prepared baking sheet. Bake in a 400º F oven until golden brown, about 15 minutes. Cool at least 5 minutes before serving.