Preheat the oven to 350°F, then place a 9-inch round cake pan or cast iron skillet in the oven just long enough to be ready for the butter coating. Watch for the pan to heat so the butter melts quickly when added.

Melt the 5 tbsp butter in the hot pan (either on the stove or directly in the oven), swirl to coat, then sprinkle brown sugar and cinnamon evenly over the butter. The surface should look evenly covered and lightly speckled.

Arrange the peach slices in overlapping concentric circles over the brown sugar layer, then set aside. Fill the pan in a tight pattern so the rings stay visible after flipping.

In a mixing bowl, beat the softened butter and granulated sugar until fluffy, about 2 minutes. The mixture should look paler and thicker, forming ribbons when you lift the beaters.

Beat in the eggs one at a time, then mix in the vanilla extract. Stop when the batter looks smooth and glossy with no streaks.

Alternately mix in the flour mixture (all-purpose flour, baking powder, salt, and 1/2 tsp cinnamon) and the whole milk or sour cream, starting and ending with the flour. Mix just until combined for a tender crumb.

Pour the batter gently over the peach arrangement and smooth the top. The peaches should stay in place beneath a thin, even layer of batter.

Bake at 350°F for 38-42 minutes until a toothpick comes out clean and the cake pulls away from the sides. Look for a lightly golden top and a set center that springs back when lightly touched.

Cool in the pan for exactly 10 minutes, then invert onto a plate. You should see caramelized brown sugar and amber-glazed peach slices release cleanly, forming concentric rings.

Serve warm with vanilla ice cream. The glaze should glisten as the first slice is lifted to reveal the moist interior.