1. Preheat the oven to 500°. In a small baking dish, toss the beets with 2 tablespoons of the vinegar and the water. Cover with foil and bake for 1 hour, or until tender. Let cool, then peel the beets and cut them into 1/4-inch wedges. Reduce the oven temperature to 350°.
2. In a small bowl, toss the hazelnuts with the simple syrup and 3/4 teaspoon each of salt and pepper. Transfer to a parchment-lined baking sheet and bake for 25 minutes, or until the syrup-covered nuts are shiny and dry. Let cool. Leave the oven on.
3. Brush both sides of the baguette slices with 2 tablespoons of the olive oil. Arrange on a baking sheet and bake for 10 minutes, or until lightly toasted. Let cool, then spread with the blue cheese.
4. In a large bowl, whisk the remaining 2 tablespoons of vinegar and 6 tablespoons of olive oil until blended. Season with salt and pepper. Add the mesclun, herbs, beets and hazelnuts; toss to coat. Transfer the salad to plates and serve with the Roquefort toasts.

Note: To make simple syrup, combine equal parts of sugar and water and simmer over moderate heat to dissolve the sugar. Refrigerate any leftover syrup.