Heat bacon grease in the bottom of a pan.
Add shallots and minced garlic to pan and sautee 1 - 2 minutes, until softened.
Deglaze with water, scraping up bits which cling to the skillet.
Add beef broth and pepper corns, bring to a boil.
In a small bowl, combine butter and corn starch, mix together.
Whisk cornstarch mixture into sauce and simmer until lightly thickened.
Whisk in mustard