In a large saute pan or pot, bring the butter over medium heat until melted. Add the sliced mushrooms and stir to coat. Cook for about 5 minutes until the mushrooms are softened and then sprinkle with salt and pepper. Remove the mushrooms to a side plate and return the pan to the burner.
Add the canola oil to the pan and bring them to medium heat. Add the onions and stir to coat. Cook the onions, stirring occasionally, for 3-5 minutes until translucent and fragrant. Add the garlic, stir, and then cook for another 30-60 seconds. Add the sliced steak to the pan and stir. Sprinkle the steak with salt and pepper. Cook the steak, stirring occasionally until just browned through, about 6-8 minutes. Sprinkle the paprika over the beef and then stir together until the beef is well coated.
Add the broth to the pan and turn up the heat to bring the broth to a strong simmer. Once simmering, add the egg noodles, reduce the heat to medium-low and cover the pan. Simmer for 7-8 minutes until the noodles are cooked. While the noodles are cooking, combine the corn starch and water in a small dish and stir together until the corn starch is dissolved. When the noodles are cooked, remove the lid from the pan and add the corn starch slurry. Stir the slurry into the broth and allow to cook uncovered for a few more minutes until the sauce is thickened. Remove the pan from heat and stir in the reserved mushrooms and the sour cream. Sprinkle with parsley and serve.