Lay a large piece of foil on a flat surface and place the beets in the center of the foil (unpeeled). Add the garlic, thyme, half the salt, half the ground pepper, and half of the vinegar. Wrap the foil around the beets and place on a baking sheet. Bake for 1 hour or until the beets are soft. Set aside and let cool until easy enough to handle.
Meanwhile, bring a large pot of water to a boil. Once boiling, add the hazelnuts and boil for 4 minutes. Drain the hazelnuts and then place the hazelnuts on a paper towel and pat dry. Once dry, place on a baking sheet and toast for 3 minutes. Remove the nuts, stir, and toast for 3 more minutes. Remove and let cool.
Once the beets are cool enough to handle, remove the skins by carefully rubbing off the skin. Add the beets to a food processor along with the toasted hazelnuts, remaining salt and pepper, remaining vinegar, and maple syrup. Blend until smooth.