Preheat oven to 400°F and grease a non-stick muffin pan generously with melted butter, brushing the bottom, sides and top.

In a measuring cup or small bowl, combine milk and lemon juice and set aside for 5-10 minutes.

Reserve ¼ cup of blueberries for putting on top then toss the remaining blueberries with the 1 extra tablespoon of oat flour - this will help prevent them from sinking.

Combine oat flour, sweet rice flour, almond flour, sugar, baking powder, baking soda, and salt in a large mixing bowl.

Whisk the eggs and vanilla extract into the milk and add it to the dry ingredients along with the melted butter and honey. Mix with a wooden spoon until just combined, but lumps still remain.

Fold in the blueberries. For optimal muffin domes, let the batter rest for 45-60 minutes before scooping into the muffin cups. This allows the flours to better soak up the ingredients and will create more domed muffins with a better rise. If you don't want to wait, you can bake them right away and they'll still be delicious, but will have flatter tops.

Scoop ¼ cup of batter into each muffin cup. Top muffins with remaining blueberries and sprinkle generously with coarse sugar.

Bake 10 minutes. Reduce heat to 375°F and bake for another 10-12 minutes, until the edges are dark golden brown and crisp and a toothpick in the center comes out clean or with just a few crumbs.

Serve immediately or store on the counter for up to 2 days (if you put them in an airtight container, they will lose their crispiness. If I do this, I warm the muffin slightly before eating. Alternatively, I store mine on a plate on the counter).