To make the vinaigrette: In a medium bowl, whisk together the Champagne vinegar, mustard, and salt and pepper to taste. While whisking, slowly drizzle in the olive oil until the mixture is well combined and slightly thickened.
In a large bowl, combine the mixed greens, pear slices, roasted hazelnuts, and crumbled Cambozola. Toss gently with the vinaigrette, and divide onto four plates.
Top each salad with shaved Gruyère and candied pecans. Sprinkle with hazelnuts and serve immediately.
Notes: More vinegar can be used in place of Champagne vinegar in the recipe.