Prick the sweet potatoes with a fork everywhere and bake at 200 degrees for 50 minutes until soft. Then let them cool down and divide them lengthwise.
Hollow out the sweet potato halves and leave a small edge of potato on the skin. Put the rest of the potatoes in a bowl.
Put the potato peels in the oven again for 10 minutes. Meanwhile, add milk to the mashed potatoes and season with salt and pepper until it is creamy. Pour this cream into the baked skins, sprinkle with cheese and put them in the oven for a last 15min until the cheese has melted.
Cut the ham into small pieces and fry it until it is crispy and then sprinkle it over the sweet potatoes. Serve with sour cream.