1 oz. dried porcini mushrooms (abt 1 C.)
3 Tbs. unsalted butter
2 Tbs. EVOO
20 oz. cremini (baby bella) mushrooms, sliced 1/4-inch thick
Kosher salt
1/3 C. finely chopped shallot
1/3 C. dry Marsala
1 Tbs. coarsely chopped fresh thyme
3/4 C. heavy cream; more for reheating
Freshly ground black pepper
2 Tbs. chopped fresh parsely
1. Soak the porcini in 1-1/2 C very hot water, stirring occasionally, until they're rehydrated, about 20 minutes. With a slotted spoon, transfer them to a cutting board and chop coarsely. Strain the soaking liquid through a coffee filter into a small bowl and set aside.
2. In a 10-inch straight sided saute pan, heat 2 Tbsp. of butter with the olive oil over medium heat. Add the cremini and 1 tsp. salt, stirring occasionally, until the mushrooms have softened and released their liquid, 5-8 minutes. Increase the heat to medium high and cook, stirring more frequently, until the mushrooms are shrunken and very well browned,8-10 minutes more.
3. Reduce the heat to medium, add the shallots and the remaining 1 Tbsp butter and cook, stirring, until the shallots are softened, 1-2 minutes. Add the Marsala, thyme, porcini, and 1/4 C. porcini-soaking liquid (reserve the remaining liquid if making ahead). Cook and stir until most of the liquid evaporates, 1-2 minutes. Stir in the parsley (unless making ahead of time) and season to taste with salt and pepper.
Make ahead:
Can make ahead and refrigerate up to 2 days ahead of time. Just before serving, reheat it in a medium saucepan over medium heat. Stir in 1 or 2 Tbs. heavy cream, letting both reduce slightly until the ragout is just loose and saucy enough to spoon around the tenderloin. Stir in the parsley.