1.Heat oil in a large, heavy-based saucepan over moderate heat. Cook onion, stirring, 4-5 minutes, or until soft. Add garlic and spices; cook, stirring, 30 seconds, or until fragrant.
2.Add lamb; cook, stirring, 2-3 minutes, or until seared. Add tomatoes and stock. Bring to the boil. Reduce heat; simmer, covered, 1 hour.
3.Add potato to curry, simmer, uncovered, 25 minutes. Add lentils; cook a further 5 minutes, or until heated.
4.Season rogan josh with salt. Top with coriander and almonds to serve.