Keep on stirring, using a wooden spatula you will move in an 8-shaped pattern. It will help stirring everywhere in the pot and prevent the cream from sticking and going bad.
This method is called "". It comes from the fact that when the cream is ready, it covers perfectly and homogeneously the wooden spoon. It is hard to do because if the heat is slightly too intense the eggs will coagulate and form chunks. Be really careful.