In a bowl, mix together onion, garlic, beefy onion soup mix, thyme, and rosemary until combined.

Spray the body of a slow cooker with cooking spray. Add HALF of the onion mixture to the cooker. Add ONE can of condensed French onion soup on top.

Pat the chuck roast with paper towels and season with kosher salt and black pepper.

In a skillet, heat vegetable oil and sear the roast on both sides until golden brown, about 5 minutes.

Place the roast into the slow cooker, top with remaining onions, and pour remaining can of French onion soup on top.

Add butter on top of the roast. Cover and cook on low for 6-8 hours or on high for 4-6 hours until tender.

Remove the roast from the cooker and shred the meat. Pour the liquid from the slow cooker into a skillet over medium heat.

Mix water with cornstarch. Once the gravy is simmering, slowly pour in the cornstarch slurry while stirring. Simmer until thickened.

Return the shredded roast to the slow cooker and top with gravy, placing it on the warm setting until ready to serve.

Serve with chopped parsley for garnish, if desired.