Preheat oven to 350°F and grease a 9-inch cake pan. Line with parchment paper.
In a bowl, whisk together flour, baking powder, baking soda, and salt until evenly mixed.
In a large bowl, beat butter and sugar until light and fluffy. This should take a few minutes.
Add eggs one at a time, mixing well after each addition. Stir in vanilla extract.
Add sour cream and milk. Mix until smooth and fully combined.
Gradually add dry ingredients into the wet mixture. Stir gently until just combined. Do not overmix.
Fold in sliced peaches carefully so they are evenly spread in the batter.
Pour batter into the prepared pan and spread evenly. Add extra peach slices on top.
Bake for 40 to 50 minutes or until a toothpick inserted in the center comes out clean.
Allow cake to cool before removing from pan and slicing.