Cut the beef against the grain into narrow 2-inch long strips about 1/2-inch thick. Pat dry and season with salt and pepper, to taste. In a large saute pan, heat 2 tablespoons of the infused olive oil over medium-high heat. Add the prepared beef and brown on all sides, about 3 to 5 minutes. Remove the meat from the pan and set aside. Add another tablespoon oil to saute pan, if needed, and add the onions. Cook until light golden, stirring and adding 1/4 cup of beef stock to deglaze the pan. Stir in the remaining beef stock and the beef with any resting juices back to the skillet and simmer for 10 minutes. Stir in the sour cream and just heat through, do not boil. Taste for seasoning and adjust, as necessary. Transfer the stroganoff to a serving platter and serve. Enjoy!