In large bowl, stir together mayonnaise, sour cream, sugar, lemon juice, lemon zest and salt until well blended. Add chicken, grapes and celery (and slivered almonds if desired) and toss to coat well. Cover and refrigerate at least 2 hours.
Spread bread with mayonnaise and mustard. Add chicken salad, lettuce and tomato.
To double recipe, bake 3 large chicken breasts at 400 degrees for 40-45 minutes. Place breasts in aluminum pan, add wine and lemon juice and drizzle with olive oil. When done, tent with foil and let rest 15 minutes, then drain liquid and continue to tent for an hour or until breasts have cooled. Dress the chicken when cooled down before placing in refrigerator overnight.