In a blender, puree the hazelnuts with the vinegars. Add the Gorgonzola and puree for 1 minute. With the motor running, add the olive oil in a steady stream. Season to taste with salt and pepper.
Wash arugula, pat dry, and separate leaves of radicchio. Break leaves into bitesized pieces.
Just before serving, toss salad greens in a bowl with enough vinaigrette to coat leaves.
c.1998, M.S. Milliken & S. Feniger, all rights reserved