A Spicy Perspective. I took a few liberties with it and below is my adaptation.
VELVET BROWNIE SWIRL CAKE
1 cup oil
1-1/3 cups buttermilk
1-1/2 teaspoons white vinegar
1 1/2 teaspoons vanilla
3 1/2 cups all purpose flour
2 cups granulated sugar
1 teaspoon baking soda
1 teaspoon baking powder
1 teaspoon salt
4 teaspoons cocoa powder
For the brownie swirl:
3 tablespoons unsweetened cocoa powder
1/2 cup chocolate chips melted
Preheat the oven to 350 degrees. Grease and flour a 12 cup bundt pan.
Using an electric mixer, beat the oil, buttermilk, eggs, vinegar and vanilla on low until well combined.
In a separate bowl, sift the flour, sugar, baking soda, baking
powder, salt and cocoa together. Slowly add them to the wet mixture
until just combined. Scrape the bowl and mix again.
For the brownie batter: Separate out 1 2/3 cups batter. Whisk 3 tablespoons
cocoa powder and the melted chocolate into the batter. Set aside.
Pour 2/3 of the remaining velvet batter into the bundt pan.
Add the brownie batter to the bundt pan and gently smooth over the top covering all areas. Do not swirl.
Pour the remaining 1/3 velvet batter over the brownie batter.
Bake for 55 minutes until set in the middle. After 55 minutes
check the center with a wooden skewer. If it comes out clean, the cake
Allow the cake to cool for at least 20 minutes in the pan. Then carefully flip it out onto a cake plate. Allow it to cool completely before adding the glaze.
I just made a simple glaze with powdered sugar, butter, milk and vanilla. I melted 1/2 cup chocolate chips and drizzled those as well.