Bake the potatoes in a 425 degree oven for 1 hour until cooked all the way through. Cut each potato in half lengthwise and scoop out the pulp. Put all the pulp into a bowl. Add 1 stick of butter, the cream, and salt and pepper to taste. Whip into mashed potatoes.
Liberally salt and pepper each potatoe skin. Put 2 tablespoons of mashed potatoes on each skin and spread evenly. Divid onion into 8 equal parts and sprinkle evenly over each shell. Add 1 tablespoon of butter to the center of each shell. Fill each potato skin with cheddar cheese.
Divide the remaining mashed potato mixture into 8 and add to shells, spreading evenly and sealing the edges as you go. Sprinkle with paprika and heat in a 350 degree oven for 20 minutes.