Chicken Salad with roast

2 tablespoons red wine vinegar 1 teaspoon Dijon mustard 1/3 cup extra-virgin olive oil 4 cups 1/2-inch cubes chicken plus 3 tablespoons drippings reserved[...]

1 roasting chicken (store bought is perfect) 2 celery ribs , chopped into tiny pieces 2 tablespoons mayonnaise (could be regular or light) 1/4 cup sour cream[...]

4 chicken breast halves , boneless and skinless (about 2 lbs) 2 tablespoons diced onions 1 celery rib , diced 1 cup grapes , sliced in half 3 tablespoons[...]