Prepare the Crumble Topping: In a small bowl, combine flour, brown sugar, and granulated sugar. Add melted butter and rub the mixture between your fingers until it resembles coarse crumbs. Set aside.

Preheat the Oven: Preheat your oven to 350°F (160°C) and grease a 9-inch loaf pan with non-stick spray or butter.

Mix Dry Ingredients: In a medium bowl, whisk together all-purpose flour, baking powder, and salt. Set this mixture aside.

Toss Blueberries in Flour: In a small bowl, gently toss fresh blueberries with a tablespoon of flour to prevent sinkage during baking.

Mix Wet Ingredients: In a mixing bowl, whisk together granulated sugar, lemon zest, vegetable oil, and lemon extract until fully combined.

Incorporate Egg and Lemon Juice: Add the egg and lemon juice to the sugar mixture, stirring until smooth.

Combine Dry and Wet Ingredients: Gradually add the flour mixture to the wet ingredients in three parts, folding gently after each addition.

Add Milk and Sour Cream: Pour in the milk and sour cream, folding them into the batter until just combined.

Fold in Blueberries: Gently stir the floured blueberries into the batter, ensuring even distribution.

Transfer to the Pan: Pour the batter into the prepared loaf pan and sprinkle the crumble topping over it evenly.

Bake the Loaf: Place the loaf in the preheated oven and bake for 60-80 minutes, or until a toothpick comes out clean.

Prepare the Glaze and Cool: Allow the loaf to cool completely, then whisk together lemon juice, melted butter, and powdered sugar for the glaze.