Spray 5-quart slow cooker with cooking spray.
Mix onions, melted butter, ¼ teaspoon of the salt and ¼ teaspoon of the pepper in slow cooker. Add 1 cup of the broth. Cover; cook on Low heat setting 8 to 10 hours or until onions are very tender and browned.
In large bowl, mix flour, remaining ¾ teaspoon salt and remaining ½ teaspoon pepper. Add beef; toss to coat. Discard any excess flour. In 12-inch skillet, heat 1 tablespoon oil over medium-high heat. Cook half of beef 5 to 7 minutes or until browned on all sides. Transfer to slow cooker; repeat with remaining 1 tablespoon oil and remaining half of beef.
Add remaining 1 cup broth to skillet; heat to boiling over medium-high heat, scraping up any browned bits on bottom of skillet. Add to slow cooker.
Add Guinness®, potatoes, carrots and thyme to slow cooker; stir. Cover; cook on Low heat setting 8 to 10 hours or until meat is tender and sauce is thickened.
Garnish with parsley.
