1/2 cup red wine vinegar
2 tablespoons crushed dried tarragon
2 tablespoons butter
4 teaspoons minced shallots
2 cups mayonnaise
1/2 teaspoon white pepper
6 (8-ounce) whole boneless chicken breasts
6 homemade or commercial sandwich buns
6 lettuce leaves
6 slices tomato, optional
Combine vinegar and tarragon in small saucepan. Bring to boil and cook until reduced by half. Melt butter in small skillet and saute shallots until tender. Combine mayonnaise, tarragon reduction, sauteed shallots and white pepper, mixing well. Set aside.
Remove all skin and fat from chicken breasts. Pound slightly with fine side of meat tenderizing mallet. Cut in half down natural seam, eliminating any cartilage at center. Season chicken to taste with salt and pepper.
Grill chicken over moderate heat to internal temperature of 180 degrees, turning once and basting with about 1 tablespoon reserved mayonnaise mixture per side. Slice and warm sandwich buns.