It originally called for 6 tablespoons of butter – but with the gelatin in a well-made stock you can cut much of that fat out and still achieve a very satisfying result.
The mix of mushrooms listed in the recipe is just a suggestion for those without wild mushrooms handy — but a good one. You could use plain mushrooms from the grocery store, but the soup will be much better if you use mushrooms with real character. They can be expensive but the difference is amazing.
If you are a knowledgeable gatherer of wild mushrooms you probably already know what kind you would like to use. All I’ll say is that I don’t think this is a good recipe to show off morels. It’s much better with Summer or Fall mushrooms.
If you are NOT a knowledgeable gatherer of wild mushrooms, don’t even think about experimenting. Get well educated on the topic before you dive in.
An experiment with rehydrated dried mushrooms turned out disappointing. The flavor was OK but the texture of the mushrooms was off-putting. If you must use dried, first rinse rehydrate and chop VERY fine before cooking. Or process them in a food processor to very small pieces or even a powder.