Right by where Moder is, a Stone Golem spawned on the side of a cliff, with no path more than a few meters in any direction.
Stone Golems are immune to frost, but you still get experience for every frost attack which lands on them. As a result, you can sit in a nearby, safe spot and just spam the Staff of Frost on them. You can refresh your food around halfway if you want to speed things up, but that's not as food efficient; really player choice.
Went with a full 24 minute rest (closer to 23 after time to get there), fresh eitr food, spam the spell until empty, wait until full again, repeat. Went from Elemental Magic 31 to 36 by the time my rest expired.
Lot, lot faster than grinding Blood Magic, though much more high touch – AFK grinding this isn't. But still, super effective.
Source: https://www.reddit.com/r/valheim/comments/10byr7y/got_lucky_best_possible_setup_for_grinding/
