Preheat the oven to 425 degrees Fahrenheit.
Whisk together the 1 tbsp ground flax seeds plus 2.5 tbsp of water in a small bowl and set aside. If you are not vegan, just sub for a real egg, this recipe works really well either way!
In a large bowl, whisk together all wet ingredients including the flax egg once thickened.
In a separate bowl, whisk together all dry ingredients aside from the blueberries.
Combine the wet with the dry and mix together with a wooden spoon until a batter forms. It should be on the thicker side.
Fold in the blueberries and mix until evenly incorporated.
Use a medium cookie scoop, spoon, or 2 tbsp and add the batter to a lined muffin tray. You want to fill them up nearly all the way. I fill them about 3/4 of the way and then use any extra batter in ones that aren't as full.
Top with additional blueberries and a sprinkle of sugar if desired.
Bake at 425 for 2 minutes, lower the oven to 350 degrees and bake for an additional 18-22 minutes. The higher initial temperature will help the muffins rise properly without drying them out. The tops should be slightly golden brown and a toothpick should come out clean when they are done. It's ok if there are a few crumbs on the toothpick, as long as it's not really wet.
Remove from the oven and let cool as is for about 10 minutes, then remove from the muffin tray to finish cooling.