Firstly, dice the lamb making sure to cut off all excess fat.
Boil the potato slices for about 10-15 minutes.
Put a splash of oil into a frying pan for the lamb (preferably a deep frying pan). Place the lamb cubes in the frying pan (all at once) as well as the onions. Stir the lamb and onions until golden brown... at this point add any vegetables you want a well as the two stock cubes (with approximately 500ml of water). Allow to simmer.
Drain the potatoes. In an individual sized pyrex dish (or casserole dish) place a layer of the potatoes on the bottom. Dribble melted butter over the potatoes.
Once the butter has been dribbled over the potatoes, pour the lamb and onions (and vegetables if using) over the potatoes. Now lay the rest of the potato slices over the top of the lamb (it may get a little bit messy) then dribble the second knob of melted butter over the top layer of the potatoes.
You can place this in the fridge if you wish to bake later; otherwise put into a preheated oven on 180 C / gas mark 4 for 45 to 60 mins or until the top layer of potatoes is golden brown.
Serve on its own and enjoy. This recipe can also be done with beef.