Preheat water to 150°F (66°C) using a sous vide machine. (I use the Anova sous vide precision cooker.)
Prepare lamb shanks by rinsing under cold water. Pat dry with paper towels and set them aside.
Mix the dry rub ingredients on a big plate. Now, prepare two sous vide bags by folding the top of each bag back over itself to form a hem. This will prevent lamb seasonings from getting on the edges of the bag. Set aside.
Place the lamb shanks on the plate and rub the mixture all over them.
Slide each lamb shank into one prepared bag. Add a couple thyme sprigs if desired. Unfold the edge before closing the bag. Vacuum seal the bags using either a vacuum sealer or a hand pump.
Lower your bagged lamb shanks into the preheated water bath, making sure the lamb is under the waterline. Cover your sous vide container with a lid to prevent the water from evaporating too fast. Set the timer for 48 hours. Check your water level a few times during cooking. Add more warm water if needed.
When the lamb is done, transfer them from the sous vide bags to a serving plate and enjoy immediately. I served them with sweet potato puree and the lamb juices from cooking.
It’s better to use heavy-duty sous vide vacuum bags instead of Ziploc bags for this recipe because of the long hours. Ziploc plastic bags might not be strong enough to securely hold your lamb for 48 hours, even at the low temperature of 150°F (66°C).