Ingredients:

  • 100g brown sugar
  • 345g all-purpose flour, divided
  • 1 tbsp ground cinnamon
  • 55g cold unsalted butter
  • 1 tsp baking powder
  • 0.5 tsp baking soda
  • 0.5 tsp kosher salt
  • 115g unsalted butter, room temperature
  • 200g granulated sugar
  • 2 large eggs, room temperature
  • 2 tsp vanilla extract
  • 240g full-fat sour cream, room temperature
  • 300g fresh or frozen blueberries

Instructions:

  1. Prepare the streusel by combining 100g brown sugar, 65g flour, and 1 tbsp cinnamon in a small bowl. Cut in 55g cold butter until the mixture resembles coarse sand. Chill in the refrigerator until needed.
  2. Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking pan or line it with parchment paper.
  3. Whisk the remaining flour (280g), baking powder, baking soda, and salt in a medium bowl. Toss the blueberries with 1 tablespoon of this dry mixture to prevent them from sinking.
  4. In a large bowl, cream 115g room-temperature butter and 200g granulated sugar together using an electric mixer until light and fluffy.
  5. Add the eggs one at a time, followed by the vanilla extract, beating well after each addition to ensure proper emulsion.
  6. Alternate adding the dry ingredients (about one-third at a time) and the sour cream (about half at a time) to the butter mixture, beginning and ending with the dry ingredients. Mix until just combined.
  7. Gently fold in the blueberries using a rubber spatula. Spread the batter into the prepared pan.
  8. Sprinkle the chilled streusel mixture evenly over the top of the batter.
  9. Bake for 45-50 minutes, or until a toothpick inserted into the center comes out clean. Allow to cool slightly before serving.