• Preheat oven to 350°F. Line two muffin pans with 18 paper liners. Set aside.

To Make The Topping:

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

To Make The Muffins:

• Whisk together 1 1/2 cups flour, baking powder, baking soda, salt, cornstarch, and nutmeg 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 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. 
• Divide the batter over the muffin pans. Add the topping. Bake for 20-22 minutes or until golden brown and a toothpick inserted in the center comes out clean. 
• Remove from oven and let cool in the tins for 5 minutes, then transfer to a wire rack to cool completely, about 1 hour. 

To Make The Maple Glaze:

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