Preheat oven to 350°F. Lightly grease a 9x5-inch loaf pan and set aside.
Peel and core the apple. Either grate it using the largest holes of a box grater or finely chop it into small pieces. I used a grater. Set aside.
In a mixing bowl, whisk together the flour, granulated sugar, brown sugar, cinnamon, baking soda, baking powder, and salt.
Stir in the beaten eggs and melted butter until a thick batter forms. Do not over mix.
Add the grated or chopped apple and the chopped nuts (if using). Stir until just combined.
Pour the batter into the prepared loaf pan and smooth the top. Sprinkle a little granulated sugar over the top if desired for added crunch.
Bake for 45-55 minutes, or until a toothpick inserted into the center of the loaf comes out clean.
Let the bread cool in the pan on a wire rack for 10 minutes. Then remove it from the pan and allow it to cool for an additional 30 minutes before slicing.