Beef in Potato Shells

3 lg baking potatoes
1 tbsp margarine
1 lb ground beef
1 can whole tomatoes, undrained
1 env taco seasoning mix
1/2 cup shredded cheddar cheese
1/2 cup sour cream

Bake potatoes as normal. Heat oven to 475*. Cut each potato lengthwise into halves.
Scoop out potatoes, leaving a 1/4-inch shell. Brush outside and inside of shells with melted butter. Place shells on ungreased cookie sheet. Bake uncovered until edges are brown, 15 to 20 minutes. Brown ground beef in 10-inch skillet. Stir in tomatoes and seasoning mix. Break up tomatoes, simmer uncovered 20 minutes, stirring occasionally. Spoon mixture into shells and sprinkle with cheese. Heat until cheese is melted. Top each with dollop of sour cream.