Peel and wash the potatoes and dice them about 1 cm. Clean and wash the leek and cut into 1 cm wide rings.
Toast the potatoes in a large stock pot in 2 tablespoons of butter. Add the leek and roast for 3 minutes. Pour in the broth, bring everything to the boil, simmer for about 8 minutes.
Cut the meat into cubes about 1 cm. Peel the banana and mash it with a fork. Add to the soup with the meat and stir. Let simmer over a low heat for about 5 minutes.
Pour in the cream, bring to the boil again and season with salt, curry and lemon juice.