~4 lbs Bone-In Legs of Lamb, defrosted, carefully trimmed of excess fat and connective tissue (10lbs total)
Adjust your oven rack to a lower-middle position and preheat the oven to 275 degrees.
Heat olive oil in a small saucepan over medium heat until hot. Add in the garlic, shallot, rosemary leaves, lemon zest, and red pepper flakes. Cook until shallots and garlic are softened, about 5 minutes.
Transfer the garlic and shallot mixture to a small bowl and add salt and pepper. Mix with a fork to combine and set aside to cool.
Once cool, rub mixture over leg of lamb.
Cook immediately or let rest uncovered in the fridge overnight to give time for the rub to absorb.
When ready to cook, place the lamb on a wire rack set in a foil-lined rimmed baking sheet. Transfer to oven and roast. Roast until an instant read thermometer inserted into the middle section of each leg of lamb reads 125-130 degrees, roughly 1.5-2 hours. Remove from oven and let rest for 40 minutes.
While the lamb is resting, increase the oven temperature to 500 degrees.
Once your oven is at temperature, return the lamb to the oven and roast until the exteriors are deep brown and crisp, roughly 15 minutes. Remove from the oven and let rest for an additional 5 minutes.
Transfer to a cutting board, and slice around the bone on each side. Once the bone is removed, slice into 1/4" slices, and serve!