• Set the oven to 350F. Lightly spray two 9-inch nonstick cake pans and line with circles of parchment at the bottom.
• Cream the bananas and sugars together until smooth, then add the rest of the wet ingredients and beat until well mixed. Scrape down the bowl as needed.
• With the mixer on low, add the baking soda and salt, then the flour, a cup at a time. Fold in the hazelnut meal. Be sure to scrape down the sides and bottom of the bowl well to ensure everything is incorporated.
• Turn the batter into the prepared pans. Bake for about 40-45 minutes, until a toothpick inserted in the center comes out moist but does not have wet batter clinging to it.
• Cool for 10 minutes in the pan, then remove the cake from the pan and continue to cool completely on a rack before frosting.
• Frost the cool cake with Nutella frosting.

For the frosting:

• Cream the butter, Nutella, sour cream, and vanilla, then beat in the sugar and cocoa powder. Mix in the heavy cream. The frosting should be thick and glossy, but spreadable. If you want to thin it down, add a bit more cream. If you want to thicken it, add a bit more sugar. Note: You can make frosting in your full sized food processor the easy way with less mess, and better, silkier results. Just dump everything in and process until smooth. Taste and adjust as needed.
• Frost the cooled cake and enjoy!