Preheat your oven to 350°F (177°C). Generously spray a muffin pan with non-stick cooking spray.

Cut 1 tbsp of cold unsalted butter into 12 pieces. Place one piece in each muffin cup and sprinkle 6 tsp of light brown sugar over it. Arrange peach slices in muffin cups.

In a mixing bowl, whisk together 1.5 cups of flour, 1 tsp of baking powder, 0.5 tsp of baking soda, and 0.25 tsp of salt.

In another bowl, beat 0.33 cups of room temperature unsalted butter with 0.67 cups of sugar until fluffy. Add 1 egg and 1 tsp of vanilla, mixing well to combine.

Gradually add half of the flour mixture to the butter mixture, stir gently, then add 0.5 cups of buttermilk. Finally, add the remaining flour and fold in cubed peaches.

Divide the batter among muffin cups, filling each about three-quarters full. Bake for 25–30 minutes, checking doneness with a toothpick.

Allow the mini cakes to cool in the pan for 5 minutes, then invert onto a wire rack to cool slightly before serving.