Fry the bacon in a saucepan, over medium heat, until cooked. Add the butter and melt.
Add the onion slices and cook until just beginning to brown, about 3-5 minutes.
Add the garlic and the sliced mushrooms and cook for about 5-6 minutes, until the mushrooms are soft.
Sprinkle the flour over the onion and mushroom mixture and stir to combine. Stir constantly for about 1 minute.
Add the broth/stock, mustard, Worcestershire sauce, salt and pepper and stir to combine. Bring to a boil, then reduce heat to a simmer.
Continue to cook until the sauce has thickened to your desired consistency, stirring frequently.
Add the heavy cream and stir to combine. Simmer for about 1-2 minutes, then remove from the heat.
Serve warm over schnitzel, potatoes, or your favorite meats.
