Lightly spray 3-4 qt slow cooker with cooking spray.
Lay out strips of sirloin and season with pepper.
Brown sirloin in olive oil over medium-high heat in a large skillet. Do this in 2-3 batches so that the meat sears nicely.
Remove beef from skillet and transfer to slow cooker.
Add butter to skillet and saute onion and mushrooms for several minutes.
Pour in can of beef consommé and stir, making sure to loosen anything stuck to the pan.
Transfer entire contents of skillet to slow cooker.
Stir in one cup of beef broth.
Cover and cook on low for 6-8 hours or until meat is tender.
Remove one cup of liquid.
Transfer mushrooms, onions, and meat into a separate bowl with a slotted spoon.
Whisk in sour cream and cream cheese until nice and smooth.
Add liquid back in until desired consistency is achieved.
Place mushrooms, onions, and meat back into slow cooker, stirring gently to distribute.
Prepare egg noodles according to package directions Stir in butter.
Serve beef stroganoff over buttered egg noodles, sprinkling with parsley if desired..