Preheat the oven to 375°F. On a wire rack set on a baking sheet, cook the bacon until crispy, about 20 minutes.
In a large skillet, melt butter over medium-high heat. Add the mushrooms and thyme, and cook, stirring, until the mushrooms brown, about 10 minutes. Add the shallots and cook, stirring, until slightly browned, about 2 minutes. Season with salt and pepper, add the stock and reduce the heat to low. Let the mushroom mixture simmer, stirring occasionally, until thickened, about 10 minutes.