1. Preheat the oven to 350F. Spray each up in a 24-muffin tin and set aside.
2. In a small bowl whisk together the flour, baking powder, salt and pumpkin pie spice.
3. In a large bowl whisk together the oil, sugar, egg, vanilla, pumpkin and milk until smooth. Then add in the flour mixture and stir until just combined.
4. Divide batter evenly amongst muffin cups. Bake for 15 to 20 minutes, or until the tops spring back when touched and a toothpick comes out clean. Allow the muffins to cool for a few minutes, then pop them out of the muffin tin.
5. Roll the muffins in the melted butter, then roll them in the cinnamon sugar. Serve!