Cut the roast chicken into small pieces and discard the skin and bones. Put the chicken, grapes, almonds, scallions and celery in a large bowl. In another bowl, mix the mayonnaise, yogurt, cream, dill, brown sugar and some salt and pepper. Pour the dressing over the salad ingredients and toss gently to combine. Taste and adjust the seasoning. Allow to chill for several hours or even overnight.
Before serving, garnish with halved grapes and chopped dill. Serve on a bed of lettuce or in a sandwich.
Preheat the oven to 400 degrees F.
Put the chicken in a roasting pan, drizzle with olive oil and sprinkle generously with salt and pepper. Roast until the juices run clear, about 1 hour 15 minutes. Let cool completely before using for chicken salad.