To prepare the vinaigrette, combine vinegars, mustard, mustard seeds, herbs and shallot in a blender. Then, on low speed, slowly incorporate each of the oils to emulsify. This vinaigrette can be made ahead and stored in the refrigerator for up to one week.
For the salad, preheat grill to medium high. Bring a pot of salted water to a rolling boil and blanch the endives (whole) for two minutes. Drain, quarter and reserve. In a non-reactive bowl, gently toss romaine, radicchio and endive in vinaigrette and allow to marinate for five minutes. Drain vegetables and reserve vinaigrette. Grill vegetables until edges are slightly charred.
Remove vegetables from grill, finish with reserved vinaigrette and diced pancetta just prior to serving.