Use this to make our Roasted Parsnip, Celery Heart, and Apple Salad.
Preheat oven to 375 degrees. Spread hazelnuts in a single layer on a rimmed baking sheet. Toast in oven until skins split and flesh turns deep golden brown, 10 to 12 minutes. While still hot, rub hazelnuts in a clean kitchen towel to remove skins (some will remain). Coarsely chop.
Heat the hazelnuts, olive oil, and shallot in a small skillet over medium heat, stirring, until shallot softens, about 2 minutes. Let cool slightly.
Stir together vinegar, lemon juice, and 3/4 teaspoon salt in a medium bowl. Whisking constantly, pour in hazelnut oil and then hazelnut mixture in a slow, steady stream; whisk until emulsified. Season with salt and pepper.