Pre Heat broiler to high, and put the oven rack 4 inches from the heat.
Use either a cast iron pan (no foil) or a broiling pan, lined with foil.
Heat pan in the broiler for one minute, (so you are not putting chicken in a cold pan in the oven).
Season the chicken with salt and pepper on both sides, and put in a pan, skin side up.
Broil, watching carefully, until the skin is golden brown, for 5 minutes.
While broiling, combine the mustard, shallots and cayenne in a bowl.
Remove chicken from oven, and turn it, skin side down.
Spread a teaspoon or so of the mustard mixture on the underside of the chicken, and broil chicken thighs another 5 minutes.
Turn the chicken again, and spread the remaining mixture on the skin side.
Broil until mustard begins to brown and skin side gets crispy, another 5 minutes.
Using a meat thermometer, make sure chicken registers 160-165 degrees F, and the juices run clear. Put the thermometer in the thickest portion of the thigh. And make sure it is not touching bone.
At this point, the chicken should be done. (If it is not done, turn off the broiler and leave the chicken in the oven 4-5 more minutes or so.)
Let the broiled chicken thighs rest or 5-10 minutes before serving. Garnish with fresh minced parsley.