Prepare the Knorr Stroganoff according to directions.
Melt 1 tablespoon of butter in a large skillet and add the chopped onion and mushrooms. Cook for 5 - 7 minutes, until tender.
Add the water and stir in the Knorr Au Jus.
Add the meatballs and cook for another 8 minutes, until meatballs are heated through and gravy has thickened.
Spread the prepared Knorr Stroganoff over the meatballs.
For the optional topping, melt the final tablespoon of butter and mix with the panko breadcrumbs. Sprinkle over the top of the stroganoff and place under the broiler for 2 - 3 minutes, until golden and crispy.
Serve and enjoy!