In a medium saucepan, melt the butter over medium heat. Add the chopped onion and sauté until translucent, about 3-4 minutes.
Add the sliced mushrooms and cook until they are browned and have released their moisture, about 5-7 minutes.
Stir in the minced garlic, thyme, and paprika, cooking for an additional minute until fragrant.
Sprinkle the flour over the mushroom mixture and stir well to combine, cooking for another minute to eliminate the raw flour taste.
Gradually pour in the beef broth, stirring constantly to avoid lumps. Bring the mixture to a simmer and let it thicken for about 5 minutes.
Reduce the heat to low and stir in the heavy cream. Simmer for another 5 minutes, allowing the sauce to become creamy.
Season with salt and pepper to taste. Garnish with chopped fresh parsley before serving.