Put potatoes into a saucepan with salt and cover with water. Cover with a lid then heat until the water is boiling then reduce to a simmer for 20-25 minutes. Drain off the water, leave the potatoes to cool briefly, peel and cut into slices.
Fry the bacon in a large frypan in hot butter until crispy then set aside.
Add the potato slices to the same frypan and fry over a medium heat until the underside is lightly browned. Turn then add the onions and fry on the other side until also brown.
Return the bacon and continue to fry until evenly heated.