This is a wonderful, easy meal. To save time, shred the cheese and crush the crackers while the chicken is browning. A bit high in calories due to the heavy cream but if anyone knows a substitution, tell me.
Adjust oven rack to lower position and heat oven to 475 degrees. Pat chicken dry with paper towels and season with salt and pepper. Heat oil in large nonstick skillet over medium-hight heat until just smoking. Brown chicken, about 3 minutes per side. Transfer chicken to 13 x 9 in baking dish, smooth side up.
Add cream, wine, 2 tsp mustard, tarragon salt and pepper to taste to skillet and bring to simmer. Remove pan from heat.
Meanwhile, spread 1 teaspoons remaining mustard on each breast, lay 1 slice of ham on top and mound each with 1/4 cup cheese. Sprinkle cracker crumbs over cheese, pressing to adhere. Pour sauce around chicken without disturbing crumbs. Bake until chicken registers 160 degrees, about 15 minutes. Serve warm.