Preheat oven to 350°F (175°C) and grease a 9x5-inch loaf pan.
Whisk flour, sugar, baking soda, baking powder, salt, and cinnamon in a large bowl.
In another bowl, whisk eggs, oil, sour cream, and vanilla until smooth.
Combine wet and dry ingredients gently until just mixed.
Fold in diced peaches and nuts if using.
Pour batter into pan and bake 50–60 minutes or until a toothpick comes out clean.
Cool in the pan 10 minutes, then transfer to a rack to cool completely.
Optional: drizzle glaze made of powdered sugar, milk, and vanilla once cooled.