01 - 
                Preheat oven to 175°C. Lightly grease a 23x13 cm loaf pan and set aside.
              
              
              
                02 - 
                Whisk together flour, baking powder, baking soda, ground cinnamon, and salt in a large bowl until fully incorporated.
              
              
              
                03 - 
                Beat softened butter and granulated sugar in a separate bowl with an electric mixer on medium speed until pale and fluffy, about 3–5 minutes.
              
              
              
                04 - 
                Incorporate eggs one at a time, beating well after each addition. Stir in vanilla extract until blended.
              
              
              
                05 - 
                Alternately add the dry ingredients and buttermilk to the creamed mixture, starting and ending with the dry ingredients. Mix until just combined—avoid overmixing.
              
              
              
                06 - 
                Gently fold diced apples and walnuts (if using) into the batter until evenly distributed.
              
              
              
                07 - 
                Mix brown sugar and the additional teaspoon of cinnamon in a small bowl to create the topping.
              
              
              
                08 - 
                Pour half the batter into prepared loaf pan. Sprinkle half the cinnamon-sugar topping evenly over batter. Add remaining batter, then top with the rest of the cinnamon-sugar mixture.
              
              
              
                09 - 
                Bake for 60–70 minutes, or until a skewer inserted into the center emerges clean.
              
              
              
                10 - 
                Allow to cool in pan for 10–15 minutes. Transfer bread to a wire rack and let cool completely before slicing.