Fry the beef and onion in a large saucepan for 5 minutes or until evenly browned, stirring to break up the meat.
Add the potatoes, garlic, ginger and spices and fry for 2 minutes, stirring.
Add the tomatoes with their juice and the stock and season with salt and pepper to taste.
Bring to the boil, then cover and simmer for 20 minutes, stirring occasionally.
Meanwhile, make the raita. Mix the yogurt, cucumber and mint together with a little seasoning. Spoon into a small bowl and chill until required.
Stir the spinach into the curry and heat through for 1 minute, then taste for seasoning.
Spoon the curry onto warmed plates and sprinkle with fresh mint leaves. Serve immediately, with the chilled raita.