Tomato soup has everything milk needs to curdle in every satisfying spoonful: acid, heat and little fat content. Low-fat dairy products like 2 percent milk don't have much stability when exposed to heat and acid -- that's how you make cottage cheese, for example -- and coagulate on contact with low-pH foods like hot tomato soup. Adding starch mixed with a fat, or roux, to the soup stabilizes the dairy proteins and prevents them from coagulating. You can use olive oil or butter; and regular flour, cornstarch or chickpea flour to keep tomato soup velvety smooth.
Heat 1 tablespoon of olive oil or butter in a saute pan over medium heat for every 2 cups of tomato soup.
Add 1 tablespoon of starch to the pan for every tablespoon of fat. Stir the fat and starch together.
Cook the roux until it turns brown, about 5 or 6 minutes, stirring occasionally. Whisk the roux into the tomato soup and bring it to a low simmer.
Simmer the soup gently for 10 minutes and lower the heat to medium-low. Measure about 1/4 cup of whole milk, 2 percent milk or skim milk for every cup of tomato soup. Add an equal amount of hot tomato soup to the milk and combine it with a whisk.
Stir the milk and soup mixture slowly and let it heat for a few minutes. Season the tomato soup to taste and serve.
Heavy cream won't separate when you add it to hot tomato soup; its fat content stabilizes the proteins and prevents them from separating. Use 1 tablespoon of heavy cream for every cup of tomato soup.
- Culinary Creation: An Introduction to Foodservice and World Cuisine; James LeRoy Morgan
A.J. Andrews' work has appeared in Food and Wine, Fricote and "BBC Good Food." He lives in Europe where he bakes with wild yeast, milks goats for cheese and prepares for the Court of Master Sommeliers level II exam. Andrews received formal training at Le Cordon Bleu.