Make the garlic and herb marinade by combining garlic, rosemary leaves, thyme, red pepper flakes, lemon zest and olive oil in food processor or blender. Pulse until well chopped, but not completely pureed.
Pat the lamb dry with paper towels, then sprinkle the salt and freshly ground pepper over the entire lamb leg. Rub the garlic and herb mixture all over the lamb.
Place the lamb leg in a vacuum seal bag or ziplock freezer bag and vacuum seal and refrigerate overnight. Let the lamb sit out to come to room temperature before cooking.
Set the sous vide temperature to 133°F / 56°C and cook the lamb for 3 to 5 hours.
When the lamb leg is almost finished, pre-heat the broiler.
Remove the lamb leg from the bag and transfer to a sheet pan. Pat dry with paper towels and rub a little olive oil over it to help promote browning. Place the lamb under the broiler until the top well browned, about 4 to 5 minutes.
Rest the lamb leg on a cutting board then slice and serve with the Italian Salsa Verde sauce. Sprinkle with finishing salt such as Maldon Sea Salt.
Place all ingredients in a blender or food processor and pulse until smooth.
Taste for seasoning and add more salt or lemon juice as needed.
Use immediately or place in a container covered with plastic wrap directly on top of the sauce to maintain the beautiful green color before refrigerating.
If a broiler isn’t available for browning the lamb, you can use a very hot heavy-bottom skillet with a little oil to sear the lamb.
The Italian Salsa Verde can be stored in the refrigerator for up to 2 days.