Rub each potato with olive oil (not extra virgin, the heat is too high in the oven and it will smoke) and give a liberal coating of salt.
Cook for 1 hour at 400 degrees. They should be soft in the middle if pierced with a knife.
When cooled, use a paring knife to slice off the top and scoop out the insides into a mixing bowl (about 90%, don’t go all the way to the skins)
Mash the scooped potato and mix in milk, butter, garlic, parmesan, chives, salt and pepper.
Fill your empty potato skins back up with the mashed potatoes and place back in the oven for about 20 minutes
Before taking out top with cheddar cheese. It should melt within 2-3 minutes (may be broiled as well)