Roll out the salt crust to approximately 8mm (1/3 inch) thick. It should be wide enough to fold over and wrap lamb completely, leaving no holes.
Place onto a preheated baking tray (260°C/500°F). Bake lamb for 45-50 minutes, remove and allow to rest for 10 minutes before breaking the crust. Break crust allowing for a further 15 minutes before serving.
Note to test for whether your lamb is properly cooked through, probe the lamb in the thickest part, it should reach medium rare at 58C/120F, resting it to medium.