In a medium saucepan over medium-high heat, melt the butter. Add the mushrooms and sauté until they have released their juices and are lightly browned, about 4 minutes. Add the shallots, garlic and thyme and sauté until fragrant, about 1 minute. Reduce the heat to low and add the flour. Cook, stirring constantly and scraping the bottom of the pan, for 5 minutes. Stir in the chicken stock. Bring the mixture to a boil and whisk constantly until incorporated. Reduce the heat to medium and simmer until slightly thickened, about 15-20 minutes.

Stir in evaporated milk or cream to soup and stir until heated through. DO NOT bring to a boil. Stir in the vinegar and season with salt and black pepper. Using an immersion blender, blitz the soup until desired consistency (this step is optional). Garnish with chopped fresh thyme and/or fresh parsley. Enjoy!