Add the sliced mushrooms, diced onion, and minced garlic to the slow cooker.
In a small bowl, whisk the vegetable broth with the flour until smooth, then pour it into the slow cooker.
Stir in the Worcestershire sauce, paprika, thyme, salt, and black pepper.
Cover and cook on low for 5 to 6 hours until the mushrooms are very tender and the sauce has thickened slightly.
Cook the egg noodles in a large pot of boiling water according to package directions, then drain.
Turn off the slow cooker and stir the sour cream into the mushroom mixture until fully combined and creamy.
Spoon the mushroom stroganoff over the cooked egg noodles and sprinkle with chopped parsley before serving.