As a way of tenderizing onions before you add them to a soup, you can boil them. For a delicate onion flavor, consider using small white or yellow varieties in your soup recipes. However, avoid Vidalia or Walla Walla varieties since they may make your soup come out overly sweet. As an alternative to boiling the onions, you can add them to a pan with butter and sauté them for several minutes until softened. Depending on your taste preferences, you can decide on the exact quantity of onions you use in the soup.
Place the onions in the fridge for 30 minutes. Chilling before preparing them will reduce the amount of sulfuric compounds released when you cut into the onions.
Rinse the onions with cold water.
Slice off the root end of each onion with a sharp kitchen knife. Reduce tearing while cutting the onion by slicing it under cold water and having a small fan blow the fumes away from you. If you use a cutting board to prepare the onions, place a small amount of white distilled vinegar on the cutting surface.
Peel the onion from the bottom of each bulb to the top.
Discard the skins while leaving the rest of the onion intact.
Move the onions into a saucepan.
Add the water and 1/4 cup milk to the pan; bring the mixture to a boil.
Cover the saucepan and simmer over low heat for approximately 20 minutes.
Drain the mixture into a colander to remove the milk and water.
Return the onions to the saucepan and cover them with 1 cup milk. Add an additional cup of milk for each serving if you are making more than a single serving of soup.
Simmer on low heat until the mixture is bubbling and the onions are fork-tender.
Add salt and pepper to taste. Remove the mixture from the heat and serve.