→ Streusel Topping
                    
                      
                        01 - 
                        6 tablespoons melted unsalted butter
                      
                    
                      
                        02 - 
                        1¼ cups plain flour
                      
                    
                      
                        03 - 
                        ¼ cup packed brown sugar
                      
                    
                      
                        04 - 
                        3 tablespoons white sugar
                      
                    
                      
                        05 - 
                        1¼ teaspoons ground cinnamon
                      
                    
                      
                        06 - 
                        ½ teaspoon powdered ginger
                      
                    
                      
                        07 - 
                        Pinch of salt
                      
                    
                      
                        08 - 
                        ⅓ cup chocolate chips (semi-sweet)
                      
                    
                      
                        09 - 
                        ⅓ cup roughly chopped walnuts (optional)
                      
                    
                  
                    → Cake Base
                    
                      
                        10 - 
                        2½ cups plain flour
                      
                    
                      
                        11 - 
                        2 teaspoons baking powder
                      
                    
                      
                        12 - 
                        ½ teaspoon baking soda
                      
                    
                      
                        13 - 
                        ½ teaspoon salt
                      
                    
                      
                        14 - 
                        1¼ cups white sugar
                      
                    
                      
                        15 - 
                        ¼ cup packed brown sugar
                      
                    
                      
                        16 - 
                        ¾ cup softened unsalted butter
                      
                    
                      
                        17 - 
                        3 room-temperature large eggs
                      
                    
                      
                        18 - 
                        2 teaspoons vanilla
                      
                    
                      
                        19 - 
                        1 teaspoon fresh lemon juice
                      
                    
                      
                        20 - 
                        1¼ cups sour cream
                      
                    
                      
                        21 - 
                        1 cup semi-sweet chocolate chips
                      
                    
                      
                        22 - 
                        ½ cup chopped walnuts (optional)