Ingredients:

  • For the Cake Batter:
  • 1 1/2 cups (190 g) all-purpose flour
  • 1 cup (200 g) granulated sugar
  • 2 teaspoons (8 g) baking powder
  • 1/2 teaspoon (3 g) fine salt
  • 1/2 cup (115 g) unsalted butter, room temperature
  • 2 large eggs, room temperature
  • 1 teaspoon (5 ml) pure vanilla extract
  • 1/2 cup (120 g) sour cream or plain Greek yogurt, room temperature
  • 1/2 cup (120 ml) whole milk (or 2% milk)
  • For the Cinnamon Swirl:
  • 1/3 cup (65 g) packed light brown sugar
  • 2 tablespoons (16 g) ground cinnamon
  • 2 tablespoons (28 g) unsalted butter, melted
  • Optional Topping / Glaze:
  • Cinnamon-sugar dusting: 1 tablespoon (12 g) granulated sugar + 1/2 teaspoon (1 g) ground cinnamon
  • Vanilla glaze: 1 cup (120 g) powdered sugar + 1–2 tablespoons (15–30 ml) milk + 1/2 teaspoon (2.5 ml) vanilla extract

Instructions:

  1. Preheat oven to 350°F (175°C). Grease and line a 9-inch round pan or an 8×8 inch square pan with parchment, or grease and flour lightly.
  2. Whisk together 1 1/2 cups all-purpose flour, 2 teaspoons baking powder, and 1/2 teaspoon fine salt in a medium bowl; set aside.
  3. In a large bowl, beat 1/2 cup room-temperature unsalted butter and 1 cup granulated sugar until light and slightly fluffy, about 2–3 minutes.
  4. Add 2 large eggs one at a time, beating briefly after each, then beat in 1 teaspoon vanilla. Stir in 1/2 cup sour cream (or Greek yogurt) until combined.
  5. Alternately add the dry mixture and 1/2 cup milk in two additions, beginning and ending with the dry ingredients; mix just until combined and avoid overmixing.
  6. In a small bowl, combine 1/3 cup packed light brown sugar, 2 tablespoons ground cinnamon, and 2 tablespoons melted butter until crumbly and moist to make the cinnamon swirl.
  7. Spoon about half the batter into the prepared pan and spread evenly. Sprinkle the cinnamon-sugar mixture evenly over the batter, reserving a little for the top if desired.
  8. Dollop the remaining batter over the cinnamon layer and spread gently to cover. Use a knife or skewer to make 3–4 figure-eight or S-shaped swirls for marbling; do not over-swirl.
  9. If using, sprinkle the top with the cinnamon-sugar dusting. Bake immediately at 350°F (175°C) for 35–45 minutes, checking at about 32 minutes.
  10. Bake until the top is golden, edges pull slightly away from the pan, and a toothpick inserted in the center comes out with a few moist crumbs.
  11. Cool the cake in the pan on a rack for 10–15 minutes, then remove to the rack to cool completely. If glazing, whisk powdered sugar, milk, and vanilla to drizzle consistency and drizzle over cooled cake; or dust with powdered sugar before serving.