Prep your loaf pan and oven: Preheat your oven to 350°F (175°C). Lightly grease a 9×5-inch loaf pan or line it with parchment paper for easy removal.

Mix the dry ingredients: In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon. Set aside.

Toss the peaches: In a small bowl, gently toss the diced peaches with 1 tablespoon of flour. This helps keep them from sinking to the bottom of the loaf during baking.

Combine wet ingredients: In a large bowl, whisk together the granulated sugar, brown sugar, egg, buttermilk, oil, and vanilla extract until smooth.

Combine everything: Add the dry ingredients to the wet mixture and stir until just combined. Gently fold in the floured peaches, being careful not to overmix.

Pour and sprinkle: Pour the batter into the prepared loaf pan. If desired, mix together the cinnamon-sugar topping and sprinkle it evenly over the top of the batter for a sweet crust.

Bake to golden perfection: Bake for 50–60 minutes or until a toothpick inserted into the center comes out clean. If the top starts to brown too quickly, loosely tent it with foil halfway through baking.

Cool and enjoy: Let the bread cool in the pan for about 10–15 minutes, then transfer to a wire rack to cool completely. Serve warm or at room temperature.