Mix flour, salt, and pepper in a large bowl and add beef cubes, tossing to coat well.

In large skillet, heat 15 mL (1 tbsp.) oil over medium-high heat. Brown beef cubes on all sides, 5 to 6 minutes, and then transfer to slow cooker.

Heat remaining oil (15 mL) in same skillet, and cook onion and mushrooms 5 to 6 minutes. Stir in tomato paste and beef broth to mix well, scraping the bottom of the skillet. Transfer this mixture to slow cooker. Cover and cook on low for 8 hours. 

Before serving, mix sour cream into beef and garnish with chives. Serve over egg noodles.