Any soup made with portobello mushrooms can be termed “portobello soup”. These dark, flavorful mushrooms can be used in a wide variety of different soups and are one of the most widely-used types of mushrooms. Preparations that are designed to accentuate the earthy flavor of portobellos are especially beloved, but many other sorts of portobello soup are also quite common. Portobello soup is also produced commercially by a number of different firms and is available in several varieties.
The portobello mushroom is the fully-developed stage in the life cycle of the common white mushroom. At this point in their development, mushrooms are quite flavorful and taste savory and satisfying when cooked. Portobello mushrooms are relatively large and are often cut down into smaller pieces for cooking. Both the stems and caps of these mushrooms can be eaten and used in portobello soup, but some cooks prefer to leave out the stems, and make use only of the mushroom caps.
Mushrooms are often blended with other savory ingredients, and many varieties of portobello soup do precisely this. Onions and mushrooms generally pair well together, and many soups are built on a base of caramelized onions and sauteed mushrooms. Meat, particularly beef, works well in this sort of soup.
The process of sauteing mushrooms in oil or butter softens their flesh. It also induces them to release liquids. This causes the flavor of mushrooms to be noticeably more pronounced in a finished soup than it would be if the mushrooms were simply boiled into a soup.
Many cream soups are built around the flavor of mushrooms, and portobello mushrooms work very well in this sort of recipe. A creamy portobello soup may be made simply by sauteing mushrooms until they are soft and flavorful and then adding stock and cream. Other creamy varieties of portobello soup can include other vegetables and spices or herbs for flavor.
Portobello soup can also be flavored with cheese. Bleu cheese blends nicely with these mushrooms, but nearly any cheese can be used to add richness to a soup. Some soups may be built on a cheese base, perhaps constructed using a roux. Other recipes may simply call for cheese to be added to a finished soup.
Soup based on portobello mushrooms is easy to make at home, but commercial varieties do exist. Cream soups are common and are often flavored with other ingredients. Varieties with onions or beef are particularly common.