Preheat the oven to 350 degrees, and line a 12-cup muffin tin with paper liners. Set aside.
In a large bowl, whisk together the flour, sugar, baking powder, and salt. In a medium bowl, whisk together the milk, eggs, maple syrup, vanilla extract, maple extract, melted butter, and sour cream.
Pour the wet ingredients into the dry mixture, and stir together with a rubber spatula. Once it is partially mixed, but some flour still remains dry, add in the blueberries and finish stirring together until there are no pockets of dry flour.
Scoop evenly into your muffin tin. Sprinkle generously with the coarse sugar. Bake for 18-20 minutes, or until the muffins are a light golden brown and a cake tester comes out clean. Cool and enjoy!