Ingredients:

  • 1 box yellow cake mix (432g)
  • 1 cup sour cream (240g)
  • 3 large eggs
  • 1/2 cup unsalted butter, melted (113g)
  • 1 tsp vanilla extract (5ml)
  • 1/2 cup brown sugar, packed (100g)
  • 1/2 cup all-purpose flour (65g)
  • 1 tbsp ground cinnamon (8g)
  • 1/4 cup unsalted butter, cold and cubed (57g)
  • 1 cup powdered sugar (120g)
  • 2 tbsp milk (30ml)
  • 1/2 tsp vanilla extract (2.5ml)

Instructions:

  1. Preheat your oven to 350°F (175°C). Grease your 9x9 inch pan with butter or line it with parchment paper.
  2. Combine the yellow cake mix, sour cream, eggs, melted butter, and vanilla in a medium bowl. Stir with a spatula until the batter is smooth and no flour streaks remain.
  3. Whisk the brown sugar, flour, and cinnamon in a separate bowl. Use your fingertips to work the cold, cubed butter into the mix until it looks like coarse sand with some pea sized lumps.
  4. Spoon the cake batter evenly into the pan.
  5. Sprinkle the cinnamon crumble over the top. Press very lightly with your palm so the topping sticks to the surface.
  6. Bake for 30–35 minutes until the top is mahogany colored and a toothpick in the center comes out clean.
  7. Let the cake rest for 15 minutes. This prevents it from falling apart when you slice it.
  8. Whisk the powdered sugar, milk, and vanilla. Drizzle the glaze over the cooled cake.