Ingredients:

  • 1 ½ cups (192g) all-purpose flour, plus more for dusting
  • ¾ cup (150g) granulated sugar
  • ¾ cup (150g) packed light brown sugar
  • 1 teaspoon ground cinnamon
  • ½ teaspoon salt
  • 1 cup (2 sticks or 227g) cold unsalted butter, cut into ½-inch cubes
  • 2 cups (256g) all-purpose flour
  • 1 teaspoon baking powder
  • ½ teaspoon baking soda
  • ½ teaspoon salt
  • ¾ cup (1 ½ sticks or 170g) unsalted butter, softened
  • 1 cup (200g) granulated sugar
  • 2 large eggs
  • 1 teaspoon pure vanilla extract
  • ¾ cup (177ml) buttermilk

Instructions:

  1. Combine flour, granulated sugar, brown sugar, cinnamon, and salt in a large bowl.
  2. Cut in the cold butter using a pastry blender or your fingertips until the mixture resembles coarse crumbs.
  3. Wrap the crumb topping and chill in the refrigerator for at least 30 minutes.
  4. Preheat the oven to 350°F (175°C). Grease and flour (or line with parchment paper) a 9-inch square baking pan.
  5. Whisk together flour, baking powder, baking soda, and salt in a medium bowl.
  6. Cream together softened butter and granulated sugar until light and fluffy.
  7. Beat in the eggs one at a time, then stir in the vanilla extract.
  8. Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk, beginning and ending with the dry ingredients. Mix until just combined. Do not overmix!
  9. Pour the cake batter into the prepared baking pan and spread evenly.
  10. Crumble the chilled topping evenly over the cake batter.
  11. Bake for 35-45 minutes, or until a toothpick inserted into the center of the cake comes out clean.
  12. Let the cake cool in the pan for at least 15 minutes before cutting and serving.