Cut the bacon into small cubes and fry in a saucepan in olive oil over a low heat until crispy. Remove and set aside. Cut the leek into small rings and sauté in the remaining fat. Dice the butter pumpkin, mix with the leek and sauté. Add the vegetable stock, bring to the boil briefly and simmer for 20 minutes. Puree with a blender. Season the soup with the spices and vinegar, pour into plates and sprinkle with the bacon cubes.