Preheat oven to 350°. Line two muffin pans with paper liners. (This recipe makes about 18 muffins.) Set aside.

Make the topping. In a small bowl, mix together sugar, brown sugar, cinnamon, flour, and a pinch salt with a fork. Mix in melted butter. Mix until small clumps form. Set aside.

Whisk together 1 1/2 cups flour, baking powder, baking soda, salt, and cornstarch in a medium bowl. Set aside. 

In another bowl, coat blueberries with the remaining 1/4 cup flour. Set aside.

In the bowl of a stand mixer, cream together butter and both sugar until light and fluffy. Add eggs and maple syrup, and mix until smooth, scraping the bowl. 

Add half of the flour mixture and mix on low until just combined. Add the buttermilk and sour cream, and mix until combined. Add the remaining flour mixture and mix until no streaks remain. Take the bowl off the mixer and add the blueberries. Gently fold through. 

Scoop batter into muffin pan. Add topping. Bake for 20 to 22 minutes or until golden brown and a toothpick comes out clean. 

Remove from oven and let cool in pan for 5 minutes, then transfer to a wire rack to cool completely. 

To make the glaze, whisk together powdered sugar, maple syrup, vanilla, and salt. If it is too thick add a splash of water, too runny another tablespoon sugar. Drizzle glaze over cooled muffins.