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

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt.

In a separate large bowl, cream together the softened butter and granulated sugar until light and fluffy.

Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract and sour cream.

Gradually add the dry mixture to the wet mixture, mixing until just combined. Fold in the diced peaches.

Pour the batter into the greased baking pan and spread it evenly.

Bake for about 30-35 minutes, until a toothpick inserted in the center comes out clean. Let it cool completely.

In a saucepan over medium heat, melt the unsalted butter and stir in the brown sugar. Cook for 2-3 minutes until smooth.

Remove from heat, add the milk, and bring to a quick boil. Once off the heat, whisk in the powdered sugar and vanilla extract until creamy.

Spread the frosting evenly over the cooled cake and let it set before slicing.