Season the lamb with salt. Heat 3 tbsp vegetable oil in a large heavy-based pan and quickly sear the lamb over a high heat, turning to colour all over. Remove to a plate.
Fry the onion and carrot in the pan, stirring over a medium heat, until golden. Add 1 tbsp vegetable oil, the celery, leek and a little salt. Stir-fry for 4-5 minutes. Add the tomato purée, ga