Preheat oven to 350 F and grease or spray your 13x9 baking dish.

Peel fresh peaches and chop into bite size pieces.

To a large mixing bowl, add the dry cake mix, melted butter, peach nectar, vanilla, and eggs. Beat with an electric mixer for 1 minute until everything is combined and the batter is thick and creamy.

Use a rubber spatula to fold in the chopped peaches.

Spread batter into prepared 13x9 pan and bake for 25-30 minutes. Use a toothpick in the center to test for doneness.

To a medium saucepan, add brown sugar, butter, and heavy whipping cream. Bring to a boil over medium-high heat, whisking to ensure all the butter is melted. Boil for 30-45 seconds, whisking constantly.

Remove from heat and whisk in vanilla (it will briefly bubble up).

Whisk in the sifted powdered sugar until icing is nice and smooth.

As soon as the cake comes out of the oven, pour the warm icing on top of the hot cake and spread it quickly.

Allow cake to cool to room temperature before serving. Refrigerating the cake for 30 minutes or so after it has cooled can help with cleaner slicing.