Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking pan.

In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt until well combined.

In a large mixing bowl, cream the softened butter and granulated sugar together using an electric mixer on medium speed until light and fluffy, about 3-4 minutes.

Add the eggs, one at a time, mixing well after each addition, then mix in the vanilla extract and sour cream until smooth.

Gradually add the dry ingredient mixture to the wet ingredients, mixing until just combined. Gently fold in your diced fresh peaches.

Pour the batter into your prepared baking pan and bake the Peach Cake in your preheated oven for 30-35 minutes, or until a toothpick comes out clean.

Allow the cake to cool in the pan for about 10 minutes, then transfer to a wire rack to cool completely.

In a saucepan over medium heat, melt the butter, then stir in the brown sugar until smooth and allow to boil for about 2 minutes.

Remove from heat and whisk in the milk, then add powdered sugar and vanilla extract, whisking until smooth.

Once the cake is cooled, spread the frosting evenly over the top and let it set for about 15 minutes before slicing.