Sauté pork and onion in butter in a large Dutch oven over low heat 5 minutes, stirring frequently. Add potatoes, water, salt, mustard, and pepper; simmer, uncovered, 30 minutes or until potatoes are tender.
Combine 1/4 cup broth from Dutch oven and flour in a small mixing bowl; stir until smooth. Stir flour mixture into pork and potato broth; cook until thickened. Serve over hot biscuits.