Place potatoes in microwave-safe dish; cover with plastic wrap, venting one corner. Microwave on HIGH 7 to 9 minutes or until just tender; set aside. Meanwhile, in large nonstick skillet, heat oil over medium-high heat; cook and stir onion 3 minutes. Add water and mustard; reduce heat to medium-low. Simmer until liquid is reduced by half; season with salt and pepper, as desired. Mash potatoes; gradually beat in milk to reach soft consistency. Season with salt and pepper, as desired. Cover and reheat briefly in microwave oven, if needed. To serve, spoon equal amounts of potatoes onto 4 individual plates; top with sausage mixture. Garnish with parsley, if desired.

Recipe Courtesy of The United States Potato Board.