Preheat the oven to 350F. Line a muffin pan with 10 parchment paper liners.
In a medium mixing bowl, whisk together the ground flaxseed and water. Let stand for 5 minutes to thicken. Then, whisk in the remaining wet ingredients (i.e., apple sauce, coconut sugar, coconut oil, maple syrup, and vanilla).
Stir in the baking soda, baking powder, sea salt, almond meal, and spelt flour into the wet mixture, one by one, in the order listed. Stop stirring when there are no flour patches at the bottom of the bowl. The batter should be quite thick and fluffy. Then, carefully fold in the frozen blueberries.
Divide the batter equally among the 10 muffin liners. (Since the batter is quite thick and fluffy, an ice cream scoop is great for this job, but you can also go the double-spoon route.)
Bake for 24 to 28 minutes, or until a toothpick inserted into the center of a muffin comes out clean.