In a medium bowl, combine flour, melted butter, and both sugars. Rub together until it resembles coarse crumbs. Set aside.

Preheat your oven to 350°F (160°C) and grease or line a 9-inch loaf pan.

In a large bowl, whisk together all-purpose flour, baking powder, and salt until well combined.

Toss fresh blueberries with a tablespoon of flour until coated to prevent sinking.

In the same bowl, combine sugar, lemon zest, vegetable oil, and lemon extract. Stir, then add egg and lemon juice, mixing until smooth.

Gradually add the dry mixture to the wet mixture, alternating with milk and sour cream. Fold gently to combine.

Fold the flour-coated blueberries into the batter evenly.

Pour the batter into the prepared loaf pan, sprinkle crumble topping on top, and bake for 60-80 minutes until a toothpick comes out clean.

Allow to cool in the pan for a few minutes, then transfer to a wire rack. Whisk glaze ingredients and drizzle over the loaf once cooled.