Preparation Method
- Preheat the oven to 325°F (170°C) with a rack set in the middle position.
- Make the cake: In a large bowl, whisk together flour, baking powder, and salt. Set aside.
- In the mixing bowl of the stand mixer fitted with the flat beater attachment, beat butter at medium-low (3–4) speed until creamy, 2–3 minutes. Increase the speed to medium (5–6). Gradually add granulated sugar and beat until light and fluffy, 2–3 minutes. Scrape down the bowl and beat until blended, about 30 seconds.
- With the mixer at medium (5–6) speed, add eggs and egg yolk one at a time, beating until well blended, about 3 minutes. Scrape down the bowl and add vanilla extract; beat until blended, about 30 seconds.
- With the mixer at low (1–2) speed, alternate adding the flour mixture and milk to the mixing bowl; add in three stages, starting and ending with the flour mixture. Increase to medium (5–6) speed and beat for 2 minutes. Scrape down the bowl and beat until blended.
- Spray a 12-cup Bundt pan with nonstick baking spray with flour.
- Make the swirl: In a small bowl, stir together brown sugar and cinnamon. Set aside.
- Pour half of the batter in the prepared pan, smoothing the top with a spatula. Sprinkle half of the swirl mixture over the batter to within ¼ inch (1 centimeter) of the edges. Repeat with half of the remaining batter and all remaining swirl mixture. Cover with the remaining batter, smoothing with a spatula.
- Bake until a cake tester comes out clean and the top is slightly golden, 50–60 minutes. Let the cake cool in the pan for 10 minutes before removing to a wire rack. Let cool completely before glazing.
- Make the glaze: In the mixing bowl of the stand mixer fitted with the whisk attachment, add confectioners’ sugar, milk, butter, vanilla bean seeds, vanilla extract, and cinnamon. Starting on medium (5–6) speed and gradually increasing to high (9–10), beat for 2 minutes. Scrape down the bowl and beat until blended, about 30 seconds. Spoon the glaze over the cake, allowing it to roll down the sides.
Pro Tip
For a different flavor profile, substitute the cinnamon with pumpkin pie spice or apple pie spice.
