Peel and dice the potatoes. Finely dice the onions and carrots and sauté in the butter until translucent. Add the potatoes and the broth. Bring everything to a boil and cook over medium heat for 7-8 minutes. Add the peas to the soup and cook for another 3 minutes. Remove half of the soup, puree with the cutting stick, put back in the saucepan and bring to the boil. Season with salt and pepper. Heat the sliced sausages in the soup.