Preheat your oven to 350°F (177°C) and generously spray the muffin pan with non-stick cooking spray to prevent sticking.

Cut the cold butter into 12 small pieces and place one piece in each muffin cup. Sprinkle the brown sugar evenly over the butter. Slice the peaches thinly, then arrange them beautifully in each cup.

In a bowl, whisk together the flour, baking powder, baking soda, and salt. In a separate mixing bowl, beat the room temperature butter and granulated sugar together until fluffy. Add the egg and vanilla extract, mixing until creamy.

Gradually add half of the flour mixture to the wet ingredients, mixing on low speed. Pour in the buttermilk, then add in the remaining flour mixture. Gently fold in the diced peaches, being careful not to overmix.

Divide the cake batter evenly among the prepared muffin cups. Bake for 25-30 minutes, or until a toothpick comes out clean from the center.

Allow the cakes to cool in the pan for about 5 minutes before inverting them onto a wire rack. Serve them warm, topped with a scoop of vanilla ice cream.