I usually take "THE Potatoes" ...
In a large bowl, mix together:
1 can cream of mushroom soup
Equal parts sour cream (equal to c of m soup)
1 medium onion, diced
3 to 4 cups shredded, sharp cheddar
1 lb bag, frozen, southern style hash browns (NOT the ones with the peppers)
Spread in a 9 x 13 baking dish and bake at 375 for 1 hour. If you leave them in the oven longer (covered), they only get better. I've also done it where I bake them at home then when we get to the party, I'll throw them in the host's oven until we're ready to eat.
BTW, the name came from all our friends asking "Are you bringing THE potatoes?" ... They might have a real name but I don't know it.