Ever eat an Eskimo Pie?
One way to make eskimo ice cream is to mix the seal oil, ground and melted caribou fat, berries, and some dried fish flakes. Mix with your hands until it gets fluffy.
You can also just take the contents of a caribou's stomach , pick out any obvious lumps (leaves, lichen, grass), and knead thoroughly. Eat as is, or mix with fish eggs and blubber.