Note: I like to make the ribs + jus the day in advance, then assemble and bake the bread right before serving.
For the beef, heat a dutch oven over medium-high heat with some olive oil and preheat the oven to 350F. Sprinkle the shortribs with salt and brown them in the olive oil on all sides until dark brown, then remove from the pot. Add the onions, garlic, and thyme to the pot and stir for 3 minutes to remove any bits from the bottom of the pot.
Return the shortribs to the onion mixture and add the broth. Cover the pot and bake for 2-3 hours until the shortribs are very tender. After 2 hours, check the pot and add more water if the ribs need to look longer; there should be ½ inch or more of liquid in the pot at all times.
When the ribs are very tender and cooked through, remove them from the pot to cool, then shred the meat and reserve for the bread. Refrigerate the cooking juices and onions until cool, scrape off the top layer of fat when the juices are chilled.
For the pull-apart bread, preheat the oven to 400F. Using a sharp bread knife, cut the bread in a criss-cross pattern to make cubes of bread, but do not cut all the way through the bread. The loaf should still be intact. Using your fingers, alternate layers of cheese and beef until the bread is completely full. Place the bread with cheese and beef on a baking sheet and bake for 15-20 minutes until bubbly and crusty.
Meanwhile, reheat the onion/garlic/beef drippings in the microwave or a small pot. When the bread is cooked drizzle with some of the onion mixture, and serve the rest on the side for dipping.
Dive in, you'll need napkins. Enjoy!