Heat the olive oil over medium-high heat in a large saucepan. Add the lamb shoulder, left on the bone, and brown it on all sides.
Transfer the browned meat to the slow cooker. Add the leeks and cook in the same pan where you browned the meat. Add a little more olive oil if necessary to prevent sticking. Stir the leeks occasionally until they become soft. Then, transfer them to the slow cooker.
Add the rest of the ingredients to the crock pot and stir everything well.
Place the lid on the slow cooker. Cook the cawl for 8 – 10 hours on low or 4 – 5 hours on high. (The meat should be very tender. The potatoes will be soft (but you don’t want them mushy) and start to break apart when stuck with a fork.)
After the desired cooking time, open the lid and turn off the cooker.
With a spoon, skim off the excess fat from the surface.
Remove the bone from the lamb (the meat will fall right off) and break up the meat with a fork. Discard the bone.
With a knife, break up the potatoes into rough pieces.
Discard the bay leaf and stir the cawl gently. Serve in a bowl with a side of bread and cheese. Enjoy!