Fry the diced onion in hot olive oil. Add the tomatoes and the finely chopped ginger and simmer for about 20 minutes.
In the meantime, peel the carrots, dice them evenly and fry them in a pan.
Now finely puree the tomatoes. Stir in the buttermilk and carrots. Season with salt, pepper and a pinch of cayenne pepper. Add a dollop of crème fraiche to garnish. Serve immediately.