Preheat oven to 400 degrees F. In a Dutch oven cook sweet potatoes and rosemary, covered, in enough boiling, lightly salted water to cover for 15 to 20 minutes or until tender; drain. Return potato mixture to Dutch oven. Mash with a potato masher or an electric mixer on low speed until smooth. Add butter and 1/2 teaspoon of the salt; gradually beat in mascarpone cheese until potatoes are light and fluffy. Set aside.
In an extra-large skillet cook ground beef, carrots, and onion over medium-high heat until meat is brown and carrots are crisp-tender. Drain off fat.
Stir wine into meat mixture. Cook and stir about 2 minutes or until liquid is evaporated. Sprinkle with flour; cook and stir for 2 minutes more. Add broth. Cook and stir until mixture is slightly thickened and bubbly. Stir in peas, soy sauce, nutmeg, and the remaining 1/4 teaspoon salt.
Lightly coat a 3-quart rectangular baking dish or eight 10- to 12-ounce ramekins with cooking spray. Transfer meat mixture to baking dish or divide evenly among ramekins. Cover completely with mashed sweet potatoes. If using ramekins, place them in a shallow baking pan or roasting pan.
Bake about 20 minutes for 3-quart dish, 15 to 20 minutes for ramekins, or until heated through and starting to brown.