- Preheat oven to 375°F.  Lightly spray a mini muffin tin with cooking spray and set aside. 
- Combine dry ingredients (flour, brown sugar, baking powder, pumpkin pie spice, and salt) in a small mixing bowl and set aside. 
- In a large mixing bowl, add egg and beat with whisk.  Add in pumpkin puree, milk, and vanilla, whisking until combined. 
- Add the flour mixture to the mixing bowl, stirring with a rubber spatula until combined.  Stir in melted butter, until everything is well mixed. 
- Scoop about 1 Tbsp of the batter into each muffin cavity. 
- Bake for 10-12 minutes, until a toothpick inserted into the center comes out clean or with a few moist crumbs. 
- Let donut holes cool on a wire cooling rack. 
- While donuts are cooling, make the cinnamon sugar topping by combining the granulated sugar and ground cinnamon in a shallow bowl. 
- Melt the butter and set aside. 
- Dip cooled donut holes, one at a time, into the melted butter (shaking off the excess), then into the cinnamon sugar mix, rolling them to coat.