If you anticipate having leftover, remove the portion of the soup you think will not be consumed immediately prior to adding the lasagna noodles for cooking and put it in an air-tight container in the fridge (or even freezer for up to 2 months). When ready to serve, place the reserved portion in a pot, bring it to boiling, then proceed with the recipe as directed, adding the lasagna noodles to cook, then the cheese, etc.