Select a casserole that is twice the volume of the water recommended on the soup mix packet. Add water to the dish. Bring to a boil. Stir in soup mix. Alternatively, use boiling water from a kettle.
Cover with a lid or cling film. Heat at HIGH until the water boils. Reduce power to MEDIUM. Heat for 3 to 4 minutes for soups with small noodles, or 7 to 8 minutes for soups with broad noodles. Stir once during heating.