Serve this dish over our Polenta and Gorgonzola as a decadent first course.
In a small bowl, soak the dried porcini in the warm water until soft, about 20 minutes. Remove, squeeze gently, and chop coarsely. Discard water and set mushrooms aside.
In a large saute pan over medium heat, melt butter with olive oil. Add the shallot and garlic and cook until slightly soft, 2 to 3 minutes.
Add the porcini and saute 1 minute. Add the cremini and cook 1 minute more. Turn up heat to medium high and add remaining mushrooms. Season with salt and pepper.
Add the chopped rosemary and stir gently until mushrooms are tender, about 5 to 7 minutes. Remove pan from heat and carefully add the cognac (you'll have some flames). Return pan to heat and allow the alcohol to cook off, about 1 minute. Cover and keep warm until ready to serve with Polenta and Gorgonzola.