recipe from joythebaker.com

     adapted from the Gourmet Cookbook

3 1/2 cups cake flour

1 Tablespoon baking powder

3/4 teaspoon baking soda

1 teaspoon salt

2 sticks (1/2 pound) unsalted butter at room temprature

2 cups sugar

4 large eggs, left at room temperature for 30 minutes

2 teaspoons vanilla extract

2 cups sour cream

1/2 teaspoon orange extract

zest of 1 large orange

4 tablespoons cocoa powder

1/2 cup chocolate chips

Put rack in the oven and preheat oven to 350 degrees F.  Butter and flour a 12 cup Bundt pan and set aside.  

Sift together flour, baking powder, baking soda and salt and set aside.

Beat together butter and sugar in a large bowl with an electric mixer at medium speed until pale and fluffy, about 3 minutes.  Add eggs one at a time, beating well after each addition, then beat in vanilla.  Reduce speed to low, add half of flour mixture, and mix until just blended.  Add sour cream, mixing until just combined, then add remaining flour mixture and mix until smooth.  

Divide the batter evenly into two bowls.  In one bowl add the orange zest and orange extract and stir to combine.  In the other  bowl add sifted cocoa powder and chocolate chips and stir to combine.  

First pour the orange batter into the buttered Bundt pan, spreading it evenly around the bottom of the pan.  Next, simply add the chocolate batter on top of the orange to cover.  No swirling is necessary, although you can swirl the batters together if you like.
 

Bake until cake is springy to the touch and a wooden pick inserted in the center comes out clean, 45 minutes to 1 hour.  

Remove from oven and cool cake in the pan for 30 minutes.  Invert onto a cooling rack and cool completely.