01 - 
                        2 cups all-purpose flour.
                      
                    
                      
                        02 - 
                        2 cups granulated sugar.
                      
                    
                      
                        03 - 
                        ¾ cup dutch-processed cocoa powder.
                      
                    
                      
                        04 - 
                        1½ teaspoons baking soda.
                      
                    
                      
                        05 - 
                        1 teaspoon baking powder.
                      
                    
                      
                        06 - 
                        1 teaspoon kosher salt.
                      
                    
                      
                        07 - 
                        2 large eggs plus 2 yolks, room temperature.
                      
                    
                      
                        08 - 
                        ½ cup vegetable oil.
                      
                    
                      
                        09 - 
                        ½ cup unsalted butter, melted.
                      
                    
                      
                        10 - 
                        ¾ cup sour cream, room temperature.
                      
                    
                      
                        11 - 
                        ¼ cup whole milk, room temperature.
                      
                    
                      
                        12 - 
                        1 cup hot coffee or water.
                      
                    
                      
                        13 - 
                        ½ cup hazelnuts, chopped.
                      
                    
                      
                        14 - 
                        1⅓ cups Nutella, divided.
                      
                    
                      
                        15 - 
                        ½ cup heavy cream, divided.
                      
                    
                      
                        16 - 
                        ¾ cup unsalted butter, room temperature.
                      
                    
                      
                        17 - 
                        3 cups powdered sugar.
                      
                    
                      
                        18 - 
                        1 teaspoon vanilla.