Mix dry ingredients: In a large bowl, sift together flour, brown sugar, pumpkin pie spice (or cinnamon), baking powder, baking soda, and salt.
Mix wet ingredients: Stir together the remaining ingredients, including buttermilk, pumpkin puree, eggs, and oil, in a separate bowl.
Combine: Pour the wet ingredients over the dry ingredients and stir gently to combine, taking care not to over-mix. The batter should be slightly lumpy.
Cook pancakes: Heat a large griddle over medium-low heat. Once the griddle has completely heated through, grease with a small amount of butter and place 1/4 cup portions of the batter on the hot griddle. Allow the pancakes to cook for 4-6 minutes per side, until golden brown. Flip the pancakes only once. Reapply a little butter before each pancake is poured.
Serve: These pumpkin pancakes are best enjoyed with a small pad of butter, warm maple syrup, and crushed nuts on top.