Preheat oven to 350F. Grease and flour your bundt pan (regular 10 cup bundt pan). I personally prefer to use baking spray for bundt pans.
Combine first 3 ingredients in a large bowl; beat with a mixer at medium speed until light and fluffy. Add eggs, beating until incorporated. Stir in 1/2 teaspoon vanilla.
In a large bowl, combine flours, powder, soda, and salt. In a small bowl, combine sour cream and 1/4 cup buttermilk. Add flour mixture and sour cream mixture alternately to butter mixture, beginning and ending with flour mixture. Stop mixture to scrape down the sides of the bowl with a spatula to incorporate all the ingredients.
In a small bowl, stir together the Nutella, cocoa powder and the espresso. Remove 2 cups vanilla batter; add to chocolate mixture, and stir.
Spoon in the batters alternately to the bundt pan. With a butter knife, gently swirl the batters together. Not too many swirls or you will ruin the pretty design.
Bake for 50-55 minutes or until a wooden pick inserted in center comes out clean. Cool cake in pan 15 minutes. Remove from pan; cool on wire rack.
Dust with powdered sugar. ENJOY!