Step 1: Preheat and Prepare

Preheat your oven to 325°F (163°C) and position the rack in the center. Butter and flour your mini Bundt cake pans to ensure the cakes don’t stick. You can also use baking spray as an alternative if you’re pressed for time.

Step 2: Bourbon-Vanilla Infusion

In a small bowl, pour 2 teaspoons of bourbon (optional) and scrape the seeds from a vanilla bean into the bowl. Stir the mixture to blend the vanilla seeds thoroughly. This will add an intense vanilla flavor to your cake.

Step 3: Dry Ingredients

In a medium bowl, whisk together 2 cups of flour, 1/4 cup of cornstarch, 2 1/2 teaspoons of baking powder, 1/2 teaspoon of baking soda, and a pinch of salt. These dry ingredients will help your cakes rise and achieve a fluffy texture.

Step 4: Wet Ingredients

In a large bowl, beat together 1 cup of room temperature salted butter, 3/4 cup of sour cream, and 1 1/2 cups of sugar using an electric mixer. Beat on medium speed until the mixture is light and fluffy, about 3-5 minutes. This creaming process is essential for aerating the batter, leading to tender cakes.

Step 5: Add Eggs and Vanilla

Add the eggs one at a time to the butter mixture, followed by the egg yolk, beating well after each addition. Then, mix in the bourbon-vanilla mixture. Your batter should be smooth and well-incorporated at this point.

Step 6: Combine Wet and Dry Ingredients

Gradually add the dry ingredients to the wet ingredients, alternating with 1/4 cup of milk. Start and end with the dry ingredients, mixing just until everything is combined. Over-mixing can lead to a denser cake, so stir just enough to bring the batter together.

Step 7: Create Chocolate Marbling

Take half of the batter and place it into a separate bowl. Mix in 1/4 cup of unsweetened cocoa powder and 2 tablespoons of milk to create your chocolate marbling mixture.

Step 8: Layer and Swirl

Start by spooning a layer of vanilla batter into each mini Bundt cake cavity. Follow this by adding a spoonful of the chocolate batter. Top with another layer of vanilla batter, and then use a knife or toothpick to swirl the two batters together to create the marbled effect.

Step 9: Bake

Bake your mini Bundt cakes for 20-25 minutes, or until a toothpick inserted into the center of the cakes comes out clean. Allow the cakes to cool in the pan for 10 minutes before inverting them onto a wire rack to cool completely.

Step 10: Prepare the Glazes

For the chocolate ganache, melt 3/4 cup of semi-sweet chocolate with 3 tablespoons of cream over low heat. Stir until smooth and glossy. For the vanilla glaze, mix together 1 cup of confectioner’s sugar with 2 tablespoons of milk. Adjust the consistency if necessary by adding more milk or sugar.

Step 11: Drizzle and Serve

Once the cakes are fully cooled, drizzle the chocolate ganache and vanilla glaze over the top of each Bundt cake. The combination of flavors and textures will result in a stunning presentation and a delightful bite.