Preheat oven to 325°F. Grease and line a 9x5" loaf pan with parchment paper

Start by making your crumble topping. In a small bowl, mix flour, sugar, cinnamon, and salt. Add in your melted butter, stirring until crumbles form. Place in the fridge to chill while you make the batter

In a medium bowl, add both sugars and lemon zest and give a quick mix. Add in flour, baking powder, and salt, mixing again.

Add in one tablespoon of your softened butter at a time, mixing in between each addition. If using a stand mixer, keep it running on low while you drop in your butter one piece at a time

Add in your eggs and mix completely. Then mix in your vanilla and sour cream

Rinse your blueberries and lightly pat dry. Add them to a bowl with 1 tbsp of flour, tossing them until coated

Set aside ½ cup of your blueberries and pour the rest into your batter, folding them in

Pour your batter into your prepared loaf pan and spread evenly within. Top with your extra blueberries and very lightly press them into the batter. They don’t have to be fully submerged, just press enough to make them stick

Remove your crumble from the fridge and sprinkle over the top

Bake your blueberry loaf for 70 minutes, until a toothpick inserted comes out clean with just a few moist crumbs

Cool in the pan for 10 minutes. Then run a knife along the edge, remove the bread, and transfer to a wire rack to cool for 45 minutes to an hour

Slice and enjoy!