Heat beef stock to a simmer in a medium saucepan over medium heat; add thyme, rosemary and mushroom stems. Simmer 30 minutes.
Heat 1 Tbs of the oil in a large skillet over medium-high heat; add bacon & green onions. Cook stirring occasionally, until bacon is crisp; add sliced mushroom caps. Cook stirring often, 3 minutes. Add 1/4 cup of the wine; heat to a simmer. Simmer 10 minutes. Add beef stock/mushroom mixture and the cream (or half-and-half) to skillet; heat to a simmer. Simmer 15 minutes.
Meanwhile, in a separate heavy skillet heat 1 Tbs of the oil over high heat until very hot, cook tenderloin slices, in batches, adding more oil if necessary until lightly browned, about 2 minutes per side. Season with salt & pepper to taste (remember bacon/prosciutto can be salty). Set aside, keep warm.
Add remaining 1/4 cup of wine to the heavy skillet the tenderloin was cooked in; cook, stirring to scrape up browned bits, until wine reduces by half, 5 minutes. Add this to the simmering mushroom sauce. If mushroom sauce seems thin - thicken with 1 tablespoon of cornstarch dissolved in 2 tablespoons of cold water. Add parsley & pepper to taste. Serve pork with sauce.