Bake the potatoes at 400 degrees until done. You can start them in the microwave to save time but finish them in the oven. Let them cool. Slice in half. Scoop the potato from the skins leaving a thin layer of potato on the skin. Run the potato through a ricer if you have one or mash the potatoes until smooth.
Cut off the root side and dark green part of the leeks. Slice in half lengthwise and wash thoroughly. Cut lengthwise again then slice. Saute the leeks in the butter on medium low heat. Add the garlic at the last 2 minutes. Remove brown bits if necessary.
Combine the leeks with the potato and remaining ingredients. Fill the skins with the mixture. You may not need all of the skins. These can be refrigerated several hours in advance.
Bake in a 400 degree oven for 30-40 minutes until golden brown. Lightly broil to brown if necessary.