Put the potatoes into a pan of lightly salted cold water and bring up to the boil. Cook for about 15-20 minutes until soft when pierced with a fork. Drain well and mash with the butter.
Whilst the potatoes are cooking, heat two tablespoons of the oil in a non-stick frying pan and fry the onions over a medium heat for about 20 minutes until lightly caramelised. When they are ready, stir though the mashed potatoes.
Add the lardons or bacon to the frying pan and cook over a medium heat until crisp. Remove with a slotted spoon and drain for a moment on kitchen paper, then stir though the potatoes.
Cook the Tenderstem in boiling water for 3 minutes until just tender. Drain and lightly fold through the mash, adding a good seasoning of salt and black pepper. Using your hands divide the mixture into 8 even sized balls. Flatten into patties, lay on a plate and chill until required.
When you are ready to eat, add the rest of the oil to a frying pan and fry the patties over a medium heat for 3-4 minutes on each side. Remove to a warmed plate whilst you fry an egg per person in the same pan.