Whisk together the flour, baking powder, baking soda, brown sugar, cinnamon, nutmeg, and salt in a large bowl.
In a separate bowl, whisk the pumpkin puree, buttermilk, egg, vanilla, and melted butter until smooth.
Pour the wet ingredients into the dry ingredients and gently stir until just combined. A few small lumps are fine; avoid overmixing so the pancakes stay light.
Heat a skillet or griddle over medium-low to medium heat and lightly butter the surface. Scoop about ⅓ cup of batter onto the skillet for each pancake.
Cook for about 2–3 minutes, or until bubbles appear across the surface and the edges look set. Flip and cook for another 1–2 minutes, until the second side is golden brown. Continue with the remaining batter.
For the cinnamon butter, mix the softened butter, cinnamon, maple syrup, powdered sugar, and salt until smooth and creamy.
Stack the warm pancakes and top with a spoonful of cinnamon butter. Drizzle with maple syrup and finish with a light dusting of powdered sugar if desired.