01 -
Preheat oven to 325°F (165°C) and position rack in the center. Butter and flour a mini Bundt pan thoroughly to prevent sticking.
02 -
Pour bourbon into a small bowl. Scrape seeds from vanilla bean into bourbon and stir to blend well. Reserve scraped vanilla bean pod for another use.
03 -
In a medium bowl, whisk together flour, cornstarch, baking powder, and baking soda until well combined.
04 -
Using an electric mixer, beat butter, sour cream, and sugar in a large bowl until light and fluffy, about 3-4 minutes.
05 -
Add eggs and egg yolk to the butter mixture one at a time, beating until well blended after each addition. Beat in the bourbon-vanilla mixture until incorporated.
06 -
Add dry mixture in 2 additions alternating with milk in 1 addition, beating just until blended after each addition. Do not overmix.
07 -
Divide batter in half. Add cocoa powder and milk to one half of the batter and mix until thoroughly incorporated.
08 -
Add the first layer of vanilla batter to mini bundt pan. Follow with a layer of chocolate batter, then add the remaining vanilla batter. Use a knife or skewer to gently swirl the batters together, creating a marbled effect.
09 -
Bake mini bundts for 20-25 minutes until a tester inserted near center comes out clean.
10 -
Cool cakes in pan on a wire rack for 10 minutes. Invert bundts onto rack and cool completely before glazing.
11 -
Melt chocolate over low heat, then stir in cream until smooth and glossy. Transfer to a piping bag for easy application.
12 -
Mix together confectioners sugar and milk until smooth and pourable.
13 -
Drizzle both chocolate and vanilla glazes onto the cooled mini bundts in an alternating pattern.