Preheat the oven to 400 degrees F.

Season the fillets with salt and pepper. Rub 1 teaspoon of the mustard over each fillet, covering completely. Wrap each fillet with 2 pieces of the proscuitto ham. Drain the potatoes. Season with salt and pepper. Divide the potatoes into 4 equal piles. Wrap each fillet with one pile of the potatoes, tightly. Cover the potatoes with a damp cloth until ready to use. Repeat the process until all of the fillets are crusted. In a large, ovenproof saute pan, heat the oil. When the oil is hot, carefully lay the fillets in the hot oil. Pan-fry for 3 to 4 minutes on the first side, or until the crust is golden. Flip the fillets over and place the pan in the oven. Cook for 4 to 6 minutes. Remove from the oven.

To serve, spoon the sauce in the center of each plate. Place the crusted fillets in the center of the sauce. Garnish with chives. Serve immediately.