Add the beans and bring to the boil and leave for several minutes for all the flavours to mix in with the stock.
Cover the Paella pan with foil and turn up the heat for a minute or so. (You will hear the rice "pop" as it is caramelising on the bottom of the pan). This is called the "Socarrat" the most highly prized part of the Paella. Covering the pan at this stage also helps finish off the cooking of the top layer of rice.