1. Saute the onions in the butter for a couple minutes.
2. Add the lamb and continue lightly frying until the pieces start to brown.
3. Add the stock, cover and simmer gently for 1/2 hour.
4. Meanwhile, prepare the sauce by stirring the water into the ground walnuts.
5. Add the pomegranate syrup and sugar and simmer gently over a low heat for 10 minutes.
6. Add the walnut sauce to the lamb, along with the seasonings and lemon juice.
7. Continue to simmer, covered, over a low heat for another 30 minutes.
8. Adjust the seasonings by adding a little sugar if the dish is too sour or more pomegranate syrup if it is too sweet.
9. Serve with basmati rice.