Preheat oven to 375 degrees then line a 12 cup muffin tin with liners and set aside.
To a small dish, add ground flaxseed and 1/4 cup + 2 Tablespoons water then stir to combine. Let sit for 5 minutes to thicken.
To a large bowl, add mashed banana, maple syrup, coconut oil, milk, and vanilla then whisk to combine. Add thickened flaxseed mixture then whisk to combine. Sprinkle the next 5 ingredients - almond flour through salt - on top then whisk until combined. Add blueberries then switch to a spatula and fold to combine.
Scoop 1/4 cup batter into prepared muffin cups (I use an ice cream scoop) then bake for 17-19 minutes or until tops are browned and a toothpick inserted into the center comes out clean.
Turn the oven OFF then crack the door open and let the muffin tin sit inside for 5 minutes. As a reminder, the tops of the muffins should be browned — they will not taste burnt! Let muffins sit in the tin for an additional 10 minutes then remove to a cooling rack to cool completely. Store on the counter for 2 days or in the refrigerator for up to 5 days.
Notes
Due to the almond flour, the tops of these muffins will be brown vs light golden brown when baked. That's fine! They don't taste burnt and are still nice and soft despite the color.
When measuring the almond flour, spoon the flour out of the bag into the measuring cup, vs scooping the measuring cup into the bag of almond flour which will compact the flour and add too much to the recipe.