Preheat the oven to 350 degrees F (175 degrees C). Spray a 9x5-inch loaf pan with cooking spray.

Whisk together sugar, melted butter, sour cream, and lemon juice in a large bowl until thoroughly blended. Mix in milk.

Stir together flour, baking powder, salt, and lemon zest in a separate bowl. Remove 2 tablespoons flour mixture and place in a third, smaller bowl with frozen blueberries; stir to coat. Stir remaining flour mixture into milk-sour cream mixture with a rubber spatula or wooden spoon, blending until just combined. Fold floured blueberries into batter and transfer into the prepared loaf pan.

Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 1 hour.

Meanwhile, mix together icing sugar, lemon juice, and lemon zest in a small bowl for the topping.

Remove loaf from the oven and immediately poke holes all over the top with a toothpick. Pour topping over the top of the loaf and let cool in the pan for 10 minutes. Remove loaf to a wire rack to cool completely.