1. Preheat oven to 350 degrees. Spread hazelnuts in a single layer on a rimmed baking sheet, and toast in the oven until skins begin to split, about 10 minutes. Remove from oven. While still warm, rub nuts vigorously with a clean kitchen towel to remove skins. Discard skins, and return nuts to baking sheet. Return to oven, and continue toasting until they are fragrant and golden, 1 minute more. Remove from oven, and let cool completely. Coarsely chop, and set aside.

2. Make the vinaigrette: Place sherry and balsamic vinegars in a small bowl, and whisk to combine. Whisk in 1/4 teaspoon salt and 1/8 teaspoon pepper. Whisking constantly, slowly pour in olive oil and then hazelnut oil in a steady stream until mixture is thick and emulsified.

3. Discard large outer leaves of endive, and separate interior leaves. Place in a large salad bowl. Quarter the pears, discarding core and seeds. Using a sharp knife, cut each quarter into 1/8-inch-thick slices, and add them to the bowl.

4. Drizzle endive and pears with half the vinaigrette, and gently toss to coat. Add toasted hazelnuts, half the cheese, and the remaining vinaigrette, and toss to combine. Add remaining 1/4 teaspoon salt and 1/8 teaspoon pepper; gently toss again. Crumble the remaining cheese on top, and serve. Alternatively, divide salad mixture among serving plates, and crumble blue cheese on top of each.