Trim the lamb if necessary. Place in a slow cooker or Instant Pot.

Add garlic paste, broth or stock, mushrooms, thyme sprigs, and salt and pepper. Stir well.

Cook on high for 3 hours or low for 6 hours (slow cooker setting if using an Instant Pot).

When the lamb has cooked, remove the thyme stalks. Spoon the lamb and mushrooms onto serving plates, and add a large spoonful (or two) of the juice from the slow cooker. Garnish with fresh thyme leaves.