Preheat the oven to 375 degrees and grease a donut pan.
Make the flax egg by mixing ground flax and water in a small bowl. Set aside for 5 minutes until the mixture has thickened.
Mix dry ingredients in a medium-sized bowl (gluten-free flour, baking powder, baking soda, salt, sugar, cinnamon, pumpkin pie spice).
Mix wet ingredients in a separate medium-sized bowl (flax egg, maple syrup, milk, applesauce, vanilla) and then combine with the dry ingredients. Mix until there are no lumps.
Spoon batter into the donut pan. You should get ~6 donuts.
Bake for 10 minutes.
Mix cinnamon sugar topping while the donuts bake and then immediately after baking, roll the donuts in it! Serve immediately!
Notes
Add the cinnamon-sugar mixture on top as soon as they come out of the oven and are still hot. This allows the sugar to sort of “melt” into the donuts so it will stick!
Serve immediately! They are honestly best when served straight out of the oven.
If you do save them as leftovers, heat them up in the microwave for 20 seconds before eating.