Ingredients:

  • 2 cups all-purpose flour (for crumbs)
  • 1 cup dark brown sugar, packed
  • 2 tsp ground cinnamon
  • 1/2 tsp salt (for crumbs)
  • 3/4 cup unsalted butter, cold and cubed
  • 2 cups all-purpose flour (for cake)
  • 1 cup granulated sugar
  • 2 tsp baking powder
  • 1/2 tsp salt (for cake)
  • 1/2 cup unsalted butter, softened
  • 2 large eggs, room temperature
  • 1 cup full-fat sour cream
  • 2 tsp vanilla extract

Instructions:

  1. In a medium bowl, whisk together 2 cups all-purpose flour, 1 cup dark brown sugar, 2 tsp cinnamon, and 1/2 tsp salt.
  2. Add cold, cubed butter to the crumb mixture. Use a pastry cutter or fork to work the butter in until the mixture forms pea-to-pebble sized clumps.
  3. Optional: Chill the crumb mixture in the refrigerator for 10 minutes if the kitchen is warm.
  4. Beat softened butter and granulated sugar on medium-high speed until pale and fluffy, approximately 3 minutes.
  5. Add eggs one at a time, beating well after each addition, then stir in the vanilla extract.
  6. Sift together the remaining 2 cups flour, baking powder, and salt.
  7. Gradually add the dry ingredients to the butter mixture, alternating with the sour cream, starting and ending with the flour. Mix on low until just combined.
  8. Line a 9x9 inch square baking pan with parchment paper.
  9. Spread the cake batter evenly in the pan and top with a thick, even layer of the prepared cinnamon crumbs.
  10. Bake for 35-45 minutes or until a toothpick inserted into the cake layer comes out clean.