Preheat oven to 350°F. Place cupcake liners in a standard, 12-cup muffin pan. Set aside.
Add the wet ingredients to a large bowl: pumpkin, coconut oil, coconut sugar, maple syrup, flax egg and vanilla. Whisk until well incorporated.
Add the dry ingredients: oat flour, baking powder, baking soda, pumpkin spice and salt (if using). Whisk together until just incorporated, making sure no flour patches remain. The batter will be thick. If needed, use a rubber spatula to fold in the last bit of flour.
Using a large scoop, scoop and drop batter evenly into the muffin pan. I use this ice cream scoop to create beautiful domed tops. If not using a scoop, use a rubber spatula to smooth batter into an even layer with a domed top. To make large, domed tops, spread batter between 8-9 muffin cups.
Bake for 20-28 minutes (on the longer spectrum for larger, fewer muffins). Mine took 24 minutes for larger muffins.
Allow muffins to cool in muffin pan placed on a cooling rack for 25 minutes. Transfer muffins directly onto the cooling rack to cool completely, about 1-2 hours, or until completely cool. Enjoy! Storing instructions below.
A Note on Homemade Oat Flour: *If using homemade oat flour, make sure to blend the flour until very fine and sift the flour to remove coarse bits of oats that could create less than ideal results. Store until needed, then measure the amount required for the recipe.**Instead of pumpkin pie spice, you can use: 1 teaspoon ground cinnamon, ½ teaspoon ground cloves, and ½ teaspoon ground nutmeg.Storing Instructions: Cool completely, then store in an airtight container for up to 1 week. Best the first 3 days.Freezing Instructions: These muffins freeze well. Store in an airtight container in the freezer for up to 1-2 months. Allow to thaw at room temperature for 30 minutes, or heat in the microwave in 10-second increments until warm.