Creating the delightful Peach Cake with Brown Sugar Frosting is straightforward when you follow these easy steps:

1. Preheat Oven: Preheat your oven to 350°F (175°C). Grease and flour a 9×13-inch baking dish or two 9-inch round cake pans.
2. Combine Dry Ingredients: In a large bowl, mix together the flour, baking powder, baking soda, salt, and optional cinnamon.
3. Beat Butter and Sugars: In a separate large bowl, beat the softened butter with granulated sugar and brown sugar until light and fluffy.
4. Add Eggs and Vanilla: Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.
5. Incorporate Buttermilk: Gradually mix in the buttermilk until fully incorporated.
6. Combine Mixtures: Gradually add the dry ingredients to the wet mixture, stirring until just combined. Be careful not to over-mix.
7. Fold in Peaches: Gently fold in the diced peaches until evenly distributed throughout the batter.
8. Pour into Baking Dish: Pour the batter into the prepared baking dish or pans, spreading it evenly.
9. Bake: Place in the preheated oven and bake for 30-35 minutes, or until a toothpick inserted comes out clean.
10. Cool the Cake: Once baked, remove from the oven and allow the cake to cool in the pan for about 20-25 minutes. Then transfer to wire racks to cool completely.

For the Frosting:

11. Cook the Brown Sugar: In a small saucepan, combine brown sugar and milk over medium heat, stirring until the sugar dissolves.
12. Cool the Mixture: Bring to a simmer, then let it boil for about 2 minutes. Allow it to cool slightly.
13. Beat Butter and Sugar: In a bowl, beat the softened butter until creamy. Gradually add cooled brown sugar mixture and powdered sugar.
14. Add Vanilla: Stir in vanilla extract and mix until smooth and spreadable.

15. Frost the Cake: Once the cake has cooled completely, spread the brown sugar frosting evenly over the top of the cake.