Preheat oven to 375 degrees (F)(or your grill)
Give your potatoes a good scrub with a paper towel or rinse them off a bit and dry.
Dice potatoes into cubes. Leaving the skin on.
You're gonna need 4 sheets of aluminum foil squares to make the packets.
On each of the four squares, place 1 tbsp. of butter (or more if you like).
Divide up the cubed potatoes and place on top of the butter on each aluminum foil square.
Evenly sprinkle minced garlic over each of the four servings (also, add onion if you're using).
Then sprinkle with kosher salt & pepper.
Pour a bit of the heavy cream onto each of the potato packets. Evenly distribute the cream as best you can. Feel free to add a bit more cream as necessary.
You may need to fold up the sides just a bit to keep the cream from drizzling off the edges.
Fold up each of the sides to make a nice little bed for the potatoes, making a square. Long sides come in first then short sides. So none of the butter and cream can escape while cooking.
Place potato packets on a baking sheet and cook for about 45 minutes (until fork tender).
*If cooking on a grill, cook for about 35-45 minutes but check them at the 30 minute mark in case your grill runs hot.
Be careful when opening the packets because the steam is gonna come outta there fast and furious. Now dig in!