How to Make It
Preheat oven to 350°F. Prepare the Basic Batter: Beat butter and sugars with an electric mixer on medium speed until light and fluffy, about 4 minutes. Add eggs and egg yolks 1 at a time, beating on medium-low after each addition. Add vanilla; beat just until incorporated. Whisk together flour, baking powder, and salt in a medium bowl. Add to butter mixture alternately with sour cream, beginning and ending with flour mixture, beating on low speed just until combined after each addition. Divide Basic Batter evenly between 2 large bowls.
Prepare the Pumpkin Spice Batter: Add flour, canned pumpkin, and pumpkin pie spice to 1 of the Basic Batter bowls; stir together until completely combined. Set aside.
Prepare the Chocolate Batter: Add cocoa, sour cream, and instant coffee granules to remaining Basic Batter bowl, and stir until smooth.
Drop large spoonfuls of the Pumpkin Spice Batter across bottom of 2 greased and floured 8- x 4-inch loaf pans. Drop large spoonfuls of the Chocolate Batter, interspersing that with the Pumpkin Spice Batter to cover the bottom of each pan. Repeat with remaining Pumpkin Spice Batter and Chocolate Batter, creating layers until all batter has been used. Swirl batters with a long pick, moving in a back-and-forth motion from one end of pan to the other.
Bake in preheated oven until a wooden pick inserted in center of each loaf comes out clean, 55 to 60 minutes. Cool in pans on a wire rack 15 minutes. Turn out onto rack to cool completely, about 45 minutes.