Ingredients:

  • 1 cup (200g) Light brown sugar, packed
  • 0.5 cup (65g) All-purpose flour
  • 1.5 tbsp Ground cinnamon
  • 1 cup (115g) Toasted walnuts, finely chopped
  • 4 tbsp (56g) Unsalted butter, cold and cubed
  • 3 cups (375g) All-purpose flour, sifted
  • 1.5 tsp Baking powder
  • 1.5 tsp Baking soda
  • 0.75 tsp Fine sea salt
  • 0.75 cup (170g) Unsalted butter, softened
  • 1.5 cups (300g) Granulated sugar
  • 3 Large eggs, room temperature
  • 1.5 tsp Pure vanilla extract
  • 1.5 cups (360g) Full-fat sour cream

Instructions:

  1. In a medium bowl, combine 200g light brown sugar, 65g all-purpose flour, 1.5 tbsp cinnamon, and 115g chopped walnuts. Incorporate 56g cold cubed butter using your fingers until the mixture reaches a coarse, pea-sized sand consistency. Set aside.
  2. In a stand mixer with a paddle attachment, cream 170g softened butter and 300g granulated sugar on medium-high for 3-5 minutes until pale and voluminous.
  3. Add 3 large eggs one at a time, ensuring each is fully incorporated, then mix in 1.5 tsp vanilla extract.
  4. Sift together 375g flour, 1.5 tsp baking powder, 1.5 tsp baking soda, and 0.75 tsp sea salt. Alternately add the dry ingredients and 360g sour cream to the mixer, beginning and ending with the flour mixture.
  5. Grease and flour a 9x13-inch baking pan. Spread half of the thick batter into the bottom and level with an offset spatula. Sprinkle half of the streusel mixture over the batter.
  6. Dollop the remaining batter over the streusel layer and smooth the top. Sprinkle the remaining streusel over the top, pressing lightly.
  7. Bake at 350°F (180°C) for 55 minutes until a tester comes out clean and the house smells like a bakery. Cool in the pan for 15 minutes before slicing.