Make the brown butter: In a small saucepan, melt the butter over medium heat. Once melted, stir frequently and watch closely for the formation of brown specs on the bottom of the pan and a nutty aroma. Once you see brown specs, stir for just a few more seconds (it browns super quickly). Remove from the heat and immediately pour into a different bowl to prevent it from burning. Let the butter cool slightly (5-10 minutes) before using.
Preheat your oven to 400°F and prepare you muffin tin.
In a large mixing bowl, whisk together the brown butter, sugar, and brown sugar.
Add in the eggs, vanilla, and lemon zest and whisk until combined and smooth.
In a separate small bowl, sift together the flour, almond flour, baking powder, baking soda, and salt.
Then add about ¼ cup of the flour mixture to the blueberries and toss to coat. This helps keep the blueberries from all sinking to the bottom of the muffins.
Add half of the dry ingredient mixture and stir until combined.
Mix in the buttermilk. Then stir in the remaining dry ingredients.
Gently stir in the blueberries.
Spoon the batter into your muffin cups so that they are about ⅔ full. Sprinkle sparkling sugar over top of each muffin if desired.
Bake at 400°F for 20-25 minutes for regular sized muffins. Rotate the pan about halfway through so that the muffins brown evenly.
Remove from the oven and let cool on a wire rack.
These are best eaten the same day. Since the muffins are so moist, they will mold quickly when left at room temperature. Store in an airtight container in the fridge for 2 to 3 days.