Preheat your oven to 350°F (177°C) and prepare a 12-cup muffin pan by spraying it with non-stick cooking spray.

Cut 1 tablespoon of cold butter into 12 equal pieces and place one piece in each muffin cup. Sprinkle ½ teaspoon of light brown sugar over the butter in each cup.

Wash and slice 1-2 peaches, arranging three slices in each muffin cup. Chop the remaining peaches into small cubes and set aside.

Whisk together the flour, baking powder, baking soda, and salt in a small bowl.

Cream together the ⅓ cup of room temperature butter and ⅔ cup of sugar in a mixing bowl for about 2 minutes. Add the egg and vanilla extract, mixing for another 2-3 minutes.

Gradually add half of the prepared flour mixture to the butter mixture, then add the buttermilk, mixing until just smooth. Fold in the remaining flour and the cubed peaches.

Evenly distribute the batter into the muffin cups, filling each about three-quarters full. Bake for 25-30 minutes.

Allow the mini cakes to cool for about 5 minutes. Loosen the edges and invert the pan onto a wire rack.

Serve the mini cakes warm, optionally with a scoop of vanilla ice cream.