Preheat oven to 350°F; grease a 9-inch cake pan.
Whisk flour, baking powder, baking soda, salt, and cinnamon.
Beat butter and sugars; add eggs, vanilla, sour cream, and milk.
Mix in dry ingredients; fold in peaches. Taste and adjust the batter.
Pour into pan; sprinkle with cinnamon-sugar topping.
Bake 35–40 minutes until a clean toothpick.
Cool 10 minutes; transfer to rack.
Serve on a white ceramic cake stand with peaches.