Preheat your oven to 350°F (175°C). Grease a 9x5-inch loaf pan with non-stick spray or line it with parchment paper.
In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon.
In a large bowl, cream the butter and sugar together until light and fluffy. Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.
Mix in the sour cream until smooth. Gradually add the dry ingredients, mixing until just combined. Avoid overmixing.
Gently fold in the diced peaches and nuts, if using.
Pour the batter into the prepared loaf pan and smooth the top.
Bake for 50-60 minutes, or until a toothpick inserted into the center comes out clean.
Allow the bread to cool in the pan for 10 minutes before transferring it to a cooling rack to cool completely.