Whisk flour, baking powder, baking soda, salt, pumpkin pie spice, and brown sugar in a large bowl.
Whisk milk, pumpkin puree, eggs, and vanilla in a second bowl. Stream in melted butter while whisking.
Fold wet ingredients into dry until just combined; a few small lumps are fine. Let batter rest 5 minutes.
Heat a nonstick skillet or griddle over medium. Lightly grease with butter or oil.
Scoop about 1/4 cup batter per pancake. Cook until bubbles form and edges look set, 2–3 minutes.
Flip and cook until golden and cooked through, 1–2 minutes more. Adjust heat as needed.
Serve warm pancakes with maple syrup. Keep finished pancakes in a 200°F oven while cooking the rest.