The pot or vessel in which one cooks on the fire is called a kli rishon. Pots, and any utensil that gets used in a pot while it is on the fire, require hagala in a kli rishon (שו”ע או”ח תנא:ה). This includes a spoon for stirring a pot, a ladle for serving, or a kitchen thermometer. A pot cover is also considered to be a utensil which is used in a kli rishon, because the steam from the pot rises and hits the cover while the food is cooking (שו”ע או”ח תנא:יד). Hagala for a utensil that absorbed beliot in a kli rishon is done in a pot on the fire with water which is bubbling (תרומת הדשן חלק א סימן קלא). When doing hagala on many utensils one after the next, one should be careful to wait long enough between immersing each utensil so that the water in the pot starts bubbling again.