Cut up pumpkin into 2 cm pieces and carrots into ½ cm pieces. Finely dice up the onion and garlic. Put everything in the slow-cooker.
Combine the tomato paste, liquid beef stock, water, and thyme in a separate bowl and set aside.
Place the lamb shanks in the slow-cooker, and add the crushed tomatoes and liquid. Add bay leaves. Put on the lid and set to cook for 6 hours on low. See notes.
In the last hour, remove the lamb shanks, cut away the meat and break up into small pieces. Place meat back into the slow-cooker and stir well.
At the end combine cornflour with a teaspoon of water, mix well then stir through the stew until thick. And remove the bay leaves.
Notes
Notes:
Two hours into the cook, you can rotate the lamb shanks if needed. This helps if some of the shanks are not covered.