In a large skillet or pan, melt Garlic Butter over medium heat. Add onion and carrot, and toss to coat with butter. Cook 3-5 minutes, or until onions are soft. Add sirloin, salt, pepper, and thyme. Brown meat until cooked through.
Add Worcestershire sauce, and stir to combine.
Meanwhile, in a separate bowl, combine mashed cauliflower with sour cream, Parmesan, melted Garlic Butter, salt, and pepper.
Top ground beef with mashed cauliflower. Sprinkle cheddar cheese over the top.
Bake at 350° F for 20-25 minutes. Garnish with fresh parsley, if desired, and serve.
