Make the French Onion Pot Roast
In a large dutch oven over medium-high heat, warm oil until shimmering hot.
Season chuck roast generously with kosher salt and freshly ground black pepper, then gently place it into the hot oil to sear each side until deeply golden brown, which will take 3-5 minutes on each side.
Remove the chuck roast from the dutch oven and place it on a separate plate. Set aside.
Turn the heat down to medium, then add the thinly sliced onions, bay leaves, and thyme and sauté until the onions turn translucent and tinged golden brown, 5-7 minutes.
Stir in tomato paste and garlic then add the flour and coat all the ingredients in it, stirring and cooking for a minute to cook out the raw flour.
Turn the heat off and quickly whisk in the white wine (for safety!), turn the heat back on to medium and whisk in the worcestershire sauce and beef broth.
Add the chuck roast back to the pot, top it with the lid, and simmer for 3-4 hours, until the beef is fork-tender and shreddable.
Taste the gravy and season with salt and pepper as needed.
Serve over mashed potatoes.
Make the Cheesy Mashed Potatoes
Peel and quarter the potatoes, then place them in a large pot filled with cold water and chicken base. Bring the pot to a boil and boil the potatoes until they are easily pierced with a fork.
Drain the pot and put the potatoes through a potato ricer into a large mixing bowl.
Stir in butter, shredded cheddar cheese, milk, garlic powder, and chives. Mix well, then season with salt and pepper to taste.