In a large bowl, combine thinly sliced onions, minced garlic, beefy onion soup mix, dried thyme, and dried rosemary. Toss gently and set aside.

Lightly coat the slow cooker with cooking spray. Spread half of the onion mixture across the bottom and pour one can of condensed French onion soup over the onions.

Pat the chuck roast dry, season with salt and pepper, and sear in a skillet with vegetable oil for about 5 minutes until browned.

Transfer the chuck roast to the slow cooker on top of the onion mixture. Top with remaining onion mixture, pour the second can of soup, and add pats of butter.

Cover and cook on low heat for 6 to 8 hours.

Shred the roast after cooking, returning it to the slow cooker to mix with the gravy.

To make gravy, simmer cooking liquid in a skillet, optionally thickening it with cornstarch.

Keep warm in the slow cooker until serving, garnished with chopped parsley.