Nutella Cake

Name: Nutella Cake
Prep time: 2 h
Cook time: 35 min
Total time: 2 h 35 min
Cuisine: American
Ingredients: 1 1/2 cup all-purpose flour; 1 1/2 cups granulated sugar; 3/4 cup Dutch-processed cocoa powder (sifted); 1 1/2 tsp baking soda; 1 tsp baking powder; 1 tsp salt; 1/4 cup vegetable oil; 3/4 cup buttermilk (room temperature); 3/4 cup hot water (or hot coffee); 2 large eggs (room temperature); 2 tsp vanilla; 6 large egg whites; 2 cup granulated sugar; 2 1/2 cups unsalted butter (cubed, room temperature but still cool); 3/4 cup Nutella; 1/2 cup heavy cream; chopped hazelnuts ((optional))