• Preheat the oven to 350°F (180°C). Generously grease an 8 X 8 baking pan with oil spray or butter. Set aside.

Making The Crumb Topping

• Mix brown sugar, granulated sugar, flour, salt, and ground cinnamon in a bowl.
• Add butter cubes and use your fingers to rub the butter into the mixture until it clamps together and resembles wet sand. Set it aside.

Making The Blueberry Buckle

• Combine flour, baking powder, lemon zest, and salt in a medium bowl and whisk well.
• Gently fold fresh blueberries into the flour mixture. If you use frozen blueberries, do not add them to the flour mixture; instead, add them to the final batter without thawing.
• Add melted butter, sour cream, sugar, and vanilla to a large bowl. Whisk well until everything is well combined. Add milk and stir well to combine.
• Add dry ingredients to wet in 2-3 parts and gently mix until combined. Do not overmix. The batter will be thick.
• Spread the batter in an even layer in the prepared pan. Top the batter with the crumb topping and lightly press the crumb so it sticks to the batter.
• Bake for 38-42 minutes or until a skewer inserted into the center comes out clean.
• Remove from the oven and let the blueberry buckle cool entirely before slicing.

Storing Suggestions

• Once the buckle is cooled completely, serve it immediately or store it at room temperature, tightly covered, for 2 days.
• The leftover Blueberry Buckle, tightly covered, can be refrigerated for up to 5 days.