Ingredients:

  • 3/4 cup (150g) light or dark brown sugar
  • 1/2 cup (250g) all-purpose flour for streusel
  • 2 tsp (5g) ground cinnamon
  • 6 tbsp (85g) cold unsalted butter, cubed
  • 1/2 cup (60g) chopped walnuts
  • 2 cups (250g) all-purpose flour for cake
  • 1 tsp (5g) baking powder
  • 1 tsp (5g) baking soda
  • 1/2 tsp (3g) fine sea salt
  • 1/2 cup (113g) unsalted butter, room temperature
  • 1 cup (200g) granulated sugar
  • 2 large eggs, room temperature
  • 1 cup (240g) full-fat sour cream
  • 1.5 tsp (7ml) pure vanilla extract

Instructions:

  1. Prep the foundation. Preheat your oven to 350°F (180°C) and grease a 9 inch square pan.
  2. Construct the streusel. Combine 3/4 cup brown sugar, 1/2 cup flour, 2 tsp cinnamon, and 1/2 cup walnuts.
  3. Cut the fat. Incorporate 6 tbsp cold cubed butter into the streusel until it looks like coarse, pea sized crumbs.
  4. Aerate dry goods. Whisk 2 cups flour, 1 tsp baking powder, 1 tsp baking soda, and 1/2 tsp salt for 60 seconds.
  5. Cream butter and sugar. Beat 1/2 cup room temp butter and 1 cup granulated sugar for 3 minutes until pale and fluffy.
  6. Emulsify the liquids. Add eggs one at a time, then stir in 1 cup sour cream and 1.5 tsp vanilla.
  7. Combine gently. Fold the dry ingredients into the wet until no white streaks remain.
  8. Layer the batter. Spread half the batter in the pan, sprinkle half the streusel, then repeat the layers.
  9. Bake to perfection. Bake for 50 minutes until a toothpick comes out with only a few moist crumbs.
  10. Cool and set. Let the cake rest in the pan for 15 minutes before transferring to a wire rack.