Preheat oven to 375°F and line a muffin tin with liners.
In a bowl, whisk together flour, baking powder, baking soda, and salt.
In a separate large bowl, mix melted butter and sugar until smooth.
Beat in eggs, vanilla, and sour cream until well combined.
Gradually mix in dry ingredients until just combined.
Gently fold in the diced peaches.
Divide batter evenly among muffin cups.
Bake for 20-25 minutes or until a toothpick comes out clean.
Let cool before serving.