If you're a sucker for Boston cream pie, then your world just got a lot better. This recipe uses Nutella to make a ganache to spread over the moist, icing-filled cake to create a rich, flavorful addition to the classic recipe.
Preheat oven to 350 degrees.
In a large mixing bowl, add the cake mix, eggs, melted butter, and water. Beat until well combined and smooth. Pour into a 10-inch spring form pan that has been coated with cooking spray. Bake for 25 minutes or until a toothpick inserted comes out clean. Run a knife around the edge of the pan and remove the outer ring. Allow to cool on a wire rack.
In a large saucepan add the sugar and cornstarch and stir until combined; add the milk and half-and-half, whisking until combined. Stir in the vanilla bean and seeds. Heat over medium heat, stirring often, until it comes to a rolling boil. Continue to cook, stirring constantly for 2-3 minutes, until it starts to thicken. Remove from the heat and pour about a cup of the filling into the beaten eggs, whisking quickly until combined. Pour the egg mixture back into the pan and return to medium heat, whisking to combine and continue to stir often, scraping all of the edges of the pan. Return to a boil and cook 2 more minutes, stirring constantly. Remove from heat and stir in the butter. Place in a metal or plastic bowl and place in the refrigerator to chill for about an hour. (Remove vanilla beans before cake assembly.)
When the cake has cooled, using a serrated knife, slice cake in half horizontally. Place top layer of cake cut side up onto a large plate or platter, spread with cream filling (don’t forget to remove vanilla beans). Place the bottom layer of cake, cut side down, on top of the cream filling, pressing gently.
Stir together the Nutella and heavy cream and heat in a microwave in 30-second increments, stirring in between until combined and smooth. Pour over the cake, spreading down and around the sides evenly. Refrigerate for 4 hours or overnight before serving.