If you already have chopped cooked chicken on hand, proceed to step 2. Otherwise, preheat the oven to 400 degrees. Place the chicken breasts skin side up in a 9 x 13 baking dish. Season the chicken with salt and pepper. Transfer to the oven and bake until the chicken is cooked through (the meat should no longer be pink and an instant-read thermometer inserted in the thickest part of the breast should read at least 165 degrees), about 40-50 minutes. Set aside to cool. Once the chicken is cool enough to handle, remove the skin and shred the meat from the bones. Discard skin and bones. Chop the meat into small, bite-size pieces. You should have 3 cups of chopped cooked chicken.

Combine the mayonnaise, creme fraiche, Dijon mustard, lemon juice and red onion in a medium bowl. Stir to combine. Fold in the chicken, celery and tarragon. Season to taste with salt and pepper. Cover tightly and transfer to the refrigerator. Chill for at least 30 minutes or up to 3 days.