to make the cake: preheat the oven to 350° grease your bundt pan very well so it won't stick

whisk the flour, cocoa powder, baking powder, baking soda, and salt together, set aside

in the bowl of a stand mixer cream the butter, Nutella, and sugar until light and fluffy

beat in the vanilla

beat in the eggs one at a time until fully incorporated

beat in the melted chocolate

alternate adding the dry ingredients and the sour cream to the egg mixture, mix just until smooth

scrape in the prepared bundt cake pan

bake in the preheated oven for 55-65 minutes or until a toothpick comes out clean

cool in the pan for 20-30 minutes then turn the pan over and gently ease the cake out of the pan

cool completely

make the ganache by warming the cream just until it almost boils, and then pouring it over the chocolate and Nutella, stir until the chocolate is melted and the ganache is smooth

cool just until it's able to be poured without it running off the cake immediately, read the notes on how to do that below