Preheat the oven to 350° F.
Pour half of the melted butter into the bottom of a casserole dish.
If you're going to sweeten your fruit, sprinkle the desired amount of sugar over your fruit, stir, and let sit for a few minutes.
Add fruit to the casserole dish, including any juices.
Dump premade cobbler mix into a bowl and add optional cinnamon, whisk to combine.
In a separate bowl, whisk together the egg, milk, and vanilla and pour over the dry cobbler mix.
Stir until it's the consistency of a thick cake (or brownie) batter.
Spoon batter over the fruit, don't worry if the mix doesn't cover all of the fruit.
Drizzle the remaining butter over the top of the cobbler batter.
Place the cobbler in a 350° F oven and bake for 30 minutes until the cobbler is set and the fruit is hot and bubbly.
Serve with vanilla ice cream, whipped cream, or a drizzle of heavy cream.