In a medium saucepan, melt butter and sauté the shallots, garlic, peppercorns, and black pepper for 2 minutes.
Add the brandy. Carefully ignite sauce and let flame for 3 or 4 minutes until the alcohol is burned off. Continue cooking for 2 to 3 minutes.
Add the cheese sauce and simmer for 3 minutes, stirring continually.
Stir in mustard. Simmer 5 minutes.
Add chopped parsley to garnish just prior to serving.