An easy, deconstructed version of a classic Chicken Cordon Bleu, all made in a single ovenproof skillet. This quick recipe features pan-seared boneless, skinless chicken breasts that are layered with slices of Swiss or Emmentaler cheese and Black Forest ham. The dish is topped with a simple, creamy sauce of whole-grain mustard and mascarpone cheese, and then finished under the broiler until the top layer of cheese is melted, golden brown, and bubbly.