To prepare potato topping, place potatoes in a saucepan; cover with water. Bring to a boil; cook 20 minutes or until very tender. Drain. Place potatoes, sour cream, and next 5 ingredients (sour cream through pepper) in a large bowl, and beat at medium speed of a mixer until smooth. Keep warm.
Preheat oven to 375°.
To prepare filling, heat oil in a large nonstick skillet over medium-high heat. Add carrot; sauté 7 minutes. Add mushrooms; sauté 5 minutes. Add 1 tablespoon sage and garlic; sauté 2 minutes. Sprinkle with flour; cook 2 minutes, stirring until well-blended. Add broth and wine; bring to a boil. Stir in tomato paste and vinegar. Add pot roast; cook 2 minutes. Spoon meat mixture into a 2-quart casserole.
Spread potato topping over meat mixture; sprinkle with paprika. Bake at 375° for 45 minutes or until golden brown.