Bring a large pot of salted water to boil. Add beets and cook until soft, about 30 minutes. Let cool slightly, then remove peel (it should come off pretty easily) and cut into thin rounds.
In a large saucepan, combine apple cider vinegar, sugar, and garlic. Bring to a boil and stir until sugar dissolves. Remove from heat and add beets, making sure they’re fully covered. Let sit for 30 minutes, turning beets halfway through if they’re not fully submerged in the vinegar.
Once beets are pickled, arrange on a platter or in a bowl. Sprinkle with blue cheese and hazelnuts.