Cut steak diagonally across grain into 1/4-inch-thick slices. Place steak and next 8 ingredients (though garlic) in a 3-quart electric slow cooker; stir well.

Lightly spoon flour into a dry measuring cup; level with a knife. Place flour in a small bowl; gradually add broth, stirring with a whisk until blended. Add broth mixture to slow cooker; stir well. Cover with lid; cook on high-heat setting 1 hour. Reduce to low-heat setting, and cook 7 to 8 hours or until steak is tender. Turn slow cooker off; remove lid. Let stroganoff stand 10 minutes. Stir in sour cream. Serve stroganoff over noodles.