Poke holes in the potatoes and bake for 10-15 minutes at 400.
Cut in half and scoop out the insides. Save the skins.
In a large bowl, mash together potato, cheeses, milk, butter, salt and pepper.
Place potato skins on a baking sheet and stuff with mashed potato mixture.
Dampen the outside of the skins with a little water and sprinkle with salt.
Return to oven for 10-15 minutes, until potatoes are crisp on the outside.