Ingredients:

  • 125g all-purpose flour
  • 100g brown sugar, packed
  • 115g cold unsalted butter, cubed
  • 1 tsp ground cinnamon
  • 0.25 tsp salt
  • 250g all-purpose flour
  • 2 tsp baking powder
  • 0.5 tsp salt
  • 115g unsalted butter, softened
  • 200g granulated sugar
  • 1 unit large egg, room temperature
  • 240g full-fat sour cream
  • 1 tsp vanilla extract
  • 1 tbsp fresh lemon zest
  • 300g fresh or frozen blueberries
  • 120g powdered sugar
  • 3 tbsp fresh lemon juice
  • 0.5 tsp lemon zest

Instructions:

  1. Preheat your oven to 350°F and grease a 9 inch square pan. In a medium bowl, combine 125g flour, 100g brown sugar, 1 tsp cinnamon, and 0.25 tsp salt. Add the 115g cold cubed butter and use your fingers or a pastry cutter to work the fat into the dry ingredients until you have pea sized crumbles. Place this in the fridge while you make the batter.
  2. In a large bowl, cream together 115g softened butter and 200g granulated sugar for at least 3 minutes until the mixture looks pale and fluffy. Add the egg, vanilla extract, and 1 tbsp lemon zest. Mix again on medium speed until well combined and smooth.
  3. Whisk together 250g flour, 2 tsp baking powder, and 0.5 tsp salt. Gradually add the dry ingredients and the 240g sour cream to the butter mixture, alternating between them. Gently fold in the 300g blueberries using a spatula until just distributed. Note: Don't overwork the batter or the cake will be tough.
  4. Spread the batter evenly into the prepared pan. Sprinkle the chilled streusel over the top, covering every corner. Bake for 45 minutes until a toothpick comes out clean. While it cools slightly, whisk 120g powdered sugar with 3 tbsp lemon juice and 0.5 tsp zest until it forms a thick, pourable glaze. Drizzle over the warm cake.