In a large skillet melt the butter over moderately low heat.
Season the pork with salt and pepper.
Raise heat to medium and add the chops to the pan and sauté for 7 minutes. Turn and cook until chops are browned and done to medium, about 7-8 minutes longer. Remove the chops and put in a warm spot.
Add the onion to the pan and cook, stirring, until soft, about 3 minutes. Add the stock and boil until it reduces to 1/2 cup, about 2 to 3 minutes.
Stir in the mustard, herbs, and 1/8 tsp pepper.
Put the chops on a platter and pour the sauce over the meat.
Notes
Food and Wine says it is OK if the pork chops are pink in the center. Trichinosis is killed at the relatively low temperature of 150°. I use a thermometer to check the center and usually leave it until it hits 160°. (Don't overcook or they will become dry.)