Ingredients:

  • 1 ½ cups All-Purpose Flour (for topping)
  • ¾ cup Light Brown Sugar (packed, for topping)
  • ¼ cup Granulated Sugar (for topping)
  • 2 teaspoons Ground Cinnamon (for topping)
  • ½ cup (1 stick) Unsalted Butter (very cold, cubed, for topping)
  • ½ cup Light Brown Sugar (packed, for swirl)
  • 1 tablespoon Ground Cinnamon (for swirl)
  • 4 tablespoons Unsalted Butter (softened, for swirl)
  • 2 ½ cups All-Purpose Flour (for batter)
  • 2 teaspoons Baking Powder
  • ½ teaspoon Baking Soda
  • ½ teaspoon Salt (fine sea salt)
  • 1 cup Unsalted Butter (softened to room temperature, for batter)
  • 1 ½ cups Granulated Sugar (for batter)
  • 3 Large Eggs (room temperature)
  • 1 teaspoon Vanilla Extract
  • 1 cup Buttermilk (room temperature)

Instructions:

  1. Preheat oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan, or line with parchment paper with an overhang.
  2. Make the Crumb Topping: Whisk dry ingredients (flour, brown sugar, granulated sugar, cinnamon) in a medium bowl. Cut in the very cold, cubed butter using a pastry blender or fingertips until coarse, pea-sized crumbs form. Set aside in the fridge.
  3. Make the Swirl Filling: Cream together the softened swirl butter, swirl brown sugar, and swirl cinnamon until well combined and paste-like. Set aside.
  4. Whisk Dry Cake Ingredients: In a separate bowl, whisk together the cake flour, baking powder, baking soda, and salt. Set aside.
  5. Cream Butter & Sugar: In the large mixing bowl, cream the softened cake butter and granulated sugar until light and fluffy (about 3–4 minutes). Scrape down the sides.
  6. Add Eggs & Vanilla: Beat in eggs one at a time, ensuring each is fully incorporated before adding the next. Mix in the vanilla extract.
  7. Alternate Wet & Dry: Gradually add the dry ingredient mixture alternately with the buttermilk to the butter mixture, beginning and ending with the dry ingredients. Mix only until just combined; do not overmix.
  8. Layer the Cake: Pour half of the cake batter into the prepared pan and smooth evenly.
  9. Add the Swirl: Drop the prepared cinnamon swirl mixture in dollops over the batter layer. Gently spread it out slightly.
  10. Top Layer: Carefully spoon the remaining batter over the swirl layer, gently smoothing the top.
  11. Apply Topping: Retrieve the chilled crumb topping and generously sprinkle it evenly over the entire surface of the cake batter.
  12. Bake: Bake for 45–55 minutes, or until a skewer inserted near the center of the cake (avoiding the thickest part of the topping) comes out clean or with moist crumbs attached.
  13. Cool: Let the cake cool in the pan on a wire rack for at least 20 minutes before slicing and serving warm or at room temperature.