Parsley sprigs (optional) Salt and pepper Rinse chicken and put in a heavy plastic food bag; add 2 tablespoons sherry. Seal bag; rotate. Chill at least 30 minutes or up to 6 hours; turn over several times. Meanwhile, thinly slice onions; wrap several slices airtight and chill up to 6 hours. In a 10to 12-inch frying pan over medium-high heat, combine remaining onion slices, wine, vinegar, and honey. Stir often until liquid evaporates. (If made ahead, cover and set aside up to 6 hours; stir over medium-high heat to warm.) Remove from heat and mix in remaining 1 tablespoon sherry. Arrange breasts in a single-layer with marinating liquid in a 9by 13-inch pan. Bake, uncovered, in a 450 F oven just until meat is white in thickest part (cut to test), 12 to 15 minutes. With a slotted spoon, transfer chicken to a warm platter. Spoon onion mixture over chicken. Garnish with reserve onion slices and parsley. Add salt and pepper to taste. Per serving: 167 cal.; 27 g protein; 1.5 g fat (0.4 g sat.); 9.4 g carbo.; 82 mg sodium; 66 mg chol.