Marble Cake

intervals stirring between each until smooth. Or melt in a double boiler. Add to the reserved cake batter along with the remaining ¼ cup buttermilk and stir until fully combined.
Dollop the chocolate batter over the plain batter in the pans. Using the tip of a knife swirl both batters together.
Bake for 30 to 35 minutes or until a toothpick inserted into the center comes out clean. Let the cakes cool in the pans for 20 minutes. Remove and cool completely on a wire rack.
For the Chocolate Buttercream
In a large bowl or the bowl of a stand mixer fitted with the paddle attachment beat the butter on medium speed for about 2 minutes until nice and creamy
Sift in the ¼ cup of cocoa powder. Add the salt and mix on low just until combined. Scrape the bowl down.
With the mixer on low beat in the confectioners sugar a few tablespoons at a time.
Then beat in the cream and vanilla. Turn speed up to medium and beat until the frosting is well combined and fluffy about 1 minute.
For the Assembly
Trim the tops of the cakes to create level layers if needed.
Place one cake layer on a cake stand or plate. Spread about ½ cup frosting over the top. Place the other cake layer on top. Spread the remaining frosting all over the top and sides of the cake. Make swoops with a spoon or offset spatula or decorate as desired. Chill for at least 1 hour or until ready to serve.