Soak the dried mushrooms in hot water until reconstituted (~30 minutes)
Drain (save the juice, consider using some of it for borscht!) Pat the mushrooms dry with paper towels (this significantly reduces the cooking time)
Chop all of the mushrooms very finely
Saute onion in butter (vegan: vegetable oil) for a few minutes
Add garlic. Saute a few more minutes.
Add all of the mushrooms. Saute until they've released most of their water – the amount of steam should significantly decrease when they're ready. This can take some time.Meanwhile, heat some beef stock in a small pot (vegan: heat hot water with better than bouillon no beef base) Add warm beef stock until covered
Mix 4 tbsp cornstarch with 1/2 cup COLD water. Mix well.
Slowly pour the cornstarch mix into your sauce while stirring well
Bring to a boil and then allow to cool off
Add mushroom juice and/or beef stock until you reach the desired consistency
