Preheat oven to 350°F (175°C). Grease a 9-inch round cake pan and line with parchment paper.
In a bowl, whisk together flour, baking powder, and salt. Set aside.
Beat butter and granulated sugar until light and fluffy (~3 mins).
Add eggs one at a time, then mix in vanilla extract.
Alternately add the dry ingredients and milk, mixing until just combined.
Gently fold in diced peaches.
Pour batter into the prepared pan.
Sprinkle brown sugar and cinnamon on top.
Bake for 40-45 mins or until a toothpick comes out clean.
Let cool in the pan for 10 mins, then transfer to a wire rack.
Serve warm or at room temperature.
