Ingredients:

  • 1/2 cup (60g) all-purpose flour
  • 1/2 cup (100g) light brown sugar, packed
  • 1 tsp (2g) ground cinnamon
  • 1/4 cup (55g) unsalted butter, cold and cubed
  • 1 1/2 cups (225g) fresh blackberries
  • 2 tbsp (30ml) lemon juice
  • 1 tbsp (12g) cornstarch
  • 2 tbsp (25g) granulated sugar
  • 2 cups (250g) all-purpose flour
  • 1 cup (200g) granulated sugar
  • 1 tbsp (12g) baking powder
  • 1/2 tsp (3g) salt
  • 3/4 cup (180g) full-fat sour cream
  • 1/2 cup (120ml) whole milk
  • 2 large eggs, room temperature
  • 1/2 cup (115g) unsalted butter, melted and cooled
  • 2 tsp (10ml) vanilla extract

Instructions:

  1. Place blackberries, lemon juice, sugar, and cornstarch in a small saucepan over medium heat.
  2. Simmer for 5-7 minutes, stirring occasionally, until the berries burst and the mixture thickens into a glossy syrup. Remove from heat and let cool slightly.
  3. In a small bowl, whisk flour, brown sugar, and cinnamon. Use a fork or pastry cutter to work in the cold cubed butter until the mixture looks like coarse wet sand with some pea-sized lumps. Set aside.
  4. In a large bowl, whisk together flour, sugar, baking powder, and salt.
  5. Stir in the sour cream, milk, eggs, melted butter, and vanilla. Whisk until the batter is smooth and no large flour streaks remain, but do not overmix.
  6. Preheat oven to 350°F (175°C) and grease an 8-inch or 9-inch square baking pan or line it with parchment paper.
  7. Pour half of the batter into the pan and smooth the top.
  8. Spoon the blackberry reduction over the batter and swirl gently with a knife.
  9. Top with the remaining batter, then sprinkle the cinnamon streusel evenly over the surface.
  10. Bake for 40 minutes or until a toothpick inserted into the center comes out clean.