Preheat your oven to 350°F.
In a large bowl, mix together the cake mix, eggs, vegetable oil, peach nectar, and orange food coloring (if using) until the batter is smooth and well combined. Gently fold in the chopped peaches, then pour the batter into a 9×12-inch baking pan that has been lightly greased or sprayed with nonstick spray. Bake for approximately 28 minutes, or until a toothpick inserted in the center comes out clean or with just a few moist crumbs—no raw batter.
To make the frosting, place the butter, heavy cream, and brown sugar in a saucepan over medium heat and bring to a boil, stirring constantly to keep it smooth. Remove the pan from the heat and stir in the vanilla extract and sifted confectioners' sugar. Whisk until the frosting is completely smooth and free of lumps—return it to low heat briefly if needed to help dissolve any remaining sugar.
Immediately pour the warm frosting over the cake, aiming to spread it evenly in one go, as it sets quickly and becomes difficult to smooth out once firm. Allow the frosting to cool and harden at room temperature or in the refrigerator before slicing and serving.