Sweet Potato Muffins — with optional add-ins

Yields 12 muffins.

1 1/2 cups (180 grams) gluten-free oat flour (see notes)
2 tablespoons (13 grams) golden flax meal
2 teaspoons pumpkin pie spice (may substitute cinnamon)
1 teaspoon baking powder
1/2 teaspoon baking soda
1/4 teaspoon kosher salt
1/2 cup (98 grams) packed brown sugar
2 eggs
1 cup (227 grams) sweet potato purée (canned works well; I have also substituted pumpkin purée)
1/2 cup (120 grams) milk of choice (see notes)
2 tablespoons melted extra virgin coconut oil (may use another neutral-tasting oil like safflower oil)
1 teaspoon vanilla extract

Preheat the oven to 350 degrees F. Grease 12 muffin cups or spray them with cooking spray. (The muffins have a tendency to stick to paper liners. If you prefer to use liners, I recommend spraying them with cooking spray to prevent sticking.)
In a mixing bowl, whisk together the oat flour, flax meal, pumpkin pie spice, baking powder, baking soda, salt, and brown sugar. In a separate large bowl, whisk the eggs and then add the sweet potato, milk, oil, and vanilla. Whisk or stir until well combined. Add the dry mixture to sweet potato mixture and mix well. Stir in the optional add-ins.
Spoon the batter into the prepared muffin cups. (I like to use an ice cream scoop to evenly and neatly portion the batter. When using chocolate chips, I add a few extra to the top.) Bake for approximately 15 minutes, or until a tester comes out clean. (Check the muffins after about 13 minutes and gently press the tops; if they feel a little mushy in the center, give them a few more minutes and check again. To avoid dry muffins, do not over-bake.). Cool in the pan for 5 minutes, and then remove to a rack and cool completely. To preserve freshness, I like to store the muffins, tightly wrapped, in the refrigerator.

You can make your own oat flour by grinding whole oats in a food processor or blender. For every 1 cup of oat flour, you'll need to start with approximately 1 1/2 cups of whole oats. Use certified gluten-free oats if necessary. Also, in this recipe, flax meal substitutes for the xanthan gum often seen in gluten-free baking by providing binding element to the batter; it also adds omega-3s and fiber.
I have used a variety of milks in the recipe including 2% and almond milk. A recent favorite is a blend of coconut and almond milk by Silk.