Wash, core and cut the peppers into small pieces. Peel and dice the onion. Heat some oil in a large saucepan and sauté the onion and pepper pieces until translucent. Remove a small part of the mixture and set aside. Deglaze the rest in the saucepan with the broth and simmer for 10 minutes.
At the same time, boil the kritharaki in well-salted water for 10 minutes and then drain.
Season the soup with salt and pepper and puree. Add the kritharaki, stir in the cream and tomato paste and bring to the boil. Mix the cornstarch with cold water and use it to thicken the soup. Add the remaining diced pepper to the soup.