Preheat the oven to 375F (190C).
Line 12 muffin tin holes with paper liners.

Mix all the crunch ingredients with your fingers until you get a coarse crumb. Set aside.

Combine the melted butter, milk, egg, egg yolk, and vanilla extract. Set aside.

Combine the flour, maple flakes, baking powder, and salt, then add the milk mixture and mix just enough to moisten.

Gently fold in the blueberries.
Divide the dough into the liners, then divide the crunch evenly over the muffins.

Bake for 18 to 20 minutes or until a toothpick inserted into the center comes out clean.

Let cool for 10 minutes in the muffin tin before transferring to a wire rack.