Preheat oven to 350°F.
Grease an 8x8 pan with baking spray and set aside.
In a large bowl, using a hand mixer, cream together sugars, butter, egg, lemon juice, and lemon zest until fluffy.
In a separate medium bowl combine flour, baking powder, and salt.
Add to the butter mixture, alternating with milk, and mixing just until combined.
In a small bowl toss blueberries with 1 tablespoon cornstarch. Using a spatula, fold into the batter and spread into the prepared pan.
In a medium bowl, combine all topping ingredients. Sprinkle on top of the batter.
Bake 40-45 minutes or until a toothpick comes out clean.
Mix the glaze ingredients until smooth, adding 1 tablespoon of lemon juice at a time. When the blueberry buckle is cold, drizzle the glaze on top.