Preheat the Oven
Preheat to 350°F (177°C). Spray a 12-cup muffin pan with non-stick cooking spray.

Prepare the Topping
Cut 1 tablespoon of butter into 12 equal pieces and place one piece in each muffin cup. Sprinkle ½ teaspoon of brown sugar over each butter piece. Slice 1–2 peaches into thin slices and arrange about 3 slices in the bottom of each muffin cup.

Prepare the Batter
Cut the remaining peaches into small cubes to make about 1 cup. In a small bowl, whisk together flour, baking powder, baking soda, and salt. In a mixing bowl, beat butter and granulated sugar until fluffy (about 2 minutes). Add egg and vanilla extract; beat for 2–3 minutes until light.

Combine and Fold
Add half the flour mixture to the butter mixture; beat on low for 1 minute. Stir in the buttermilk, then mix for another minute. Add the remaining flour mixture and beat until just combined. Fold in the cubed peaches gently.

Fill and Bake
Divide the batter evenly among the muffin cups. Bake for 25–30 minutes or until a toothpick inserted in the center comes out clean.

Cool and Invert
Cool for 5 minutes in the pan. Run a butter knife around each cake’s edge, place a wire rack on top of the pan, and carefully invert to release the cakes.

Serve
Serve warm, optionally with vanilla ice cream or whipped cream.