Preheat your oven to 350F, and line a muffin tin with 12 liners. (I don't recommend making these without a liner, as grain-free baking is extra prone to sticking.)
In a large bowl, combine the almond butter, flax, pumpkin, sugar, eggs, baking powder, salt, and pumpkin pie spice. Stir well, until the batter is completely smooth.
Fold in any of the optional add-ins you want to. Using roughly a 1/4 cup measure, distribute the batter evenly among the 12 baking cups.
Bake for 25 to 30 minutes at 350F, until the centers puff up, and are firm to a light touch.
Allow the muffins to cool in the pan for 15 minutes, then transfer to a wire rack to cool completely.
Because these muffins are pretty moist, I recommend storing them in the fridge for the best shelf life. They will keep well in an airtight container in the fridge for up to 5 days. Or you can freeze them for up to 3 months.
You can make your own Pumpkin Pie Spice by using 1 1/2 teaspoons ground cinnamon, 1/2 teaspoon ground ginger, and 1/8 teaspoon ground cloves instead.If you don't have almond butter on hand, you can use cashew butter with similar flavor results. Sunflower butter might work as a nut-free option, too, but the flavor will be affected slightly.If you don't mind a more "wet" muffin, you can swap 1/3 cup of maple syrup for the coconut sugar.