How to Make It
In a saucepan, cover the beets with water and bring to a boil. Cook over moderate heat, adding more water as needed to keep the beets covered, until they are tender, about 1 hour. Drain the beets and let them cool. Peel the beets and slice into thin wedges.
In a bowl, whisk the olive oil and hazelnut oil with the lemon juice and honey. Season with salt. Add the beets and onion and toss to coat. Cover and refrigerate overnight, stirring once or twice. Garnish the salad with mint and serve.