In a large skillet melt butter until foamy. Add onions and sauté for a few minutes until golden and soft. Add mushrooms and stir until well coated. Brown for 5-6 minutes.
Pour in ravioli, tossing to mix everything together.
Add beef stock, mix well. Cover and let cook for 5-8 minutes, or until ravioli are cooked, stirring half way through.
Pour in cream, mix until well blended. Remove from heat.
Stir in sour cream and season with salt and pepper to taste.