Preheat oven to 350°F (175°C). Melt butter and brown sugar in skillet over medium heat. Stir until bubbly and thickened, about 2-3 minutes. Arrange peach slices on top.

In a large bowl, cream together softened butter and granulated sugar with an electric mixer until fluffy, about 3-5 minutes. Add eggs one at a time, mixing well after each, then add vanilla.

In another bowl, sift together flour, baking powder, and salt. Gradually add to creamed mixture, alternating with milk, mixing until just combined.

Pour batter over caramelized peaches, smoothing evenly without disturbing the peaches.

Bake for 35-40 minutes. Check doneness with a toothpick; it should come out clean.

Cool in the pan for 10 minutes. Run a knife around edges and invert onto a serving plate.

Serve warm or at room temperature, optionally with whipped cream or vanilla ice cream.