In a baking dish, marinate short ribs in ¼ cup Worcestershire sauce, ¼ cup beef broth, a sprinkle of fresh thyme and salt and pepper to taste. Set aside.

¼ cup beef broth, a sprinkle of fresh thyme and salt

Reduce heat to medium-low and add sugar and 1 tbsp Worcestershire sauce. Mix and simmer for 8-10 more minutes, until onions are golden brown.

Add minced garlic and cook for 1-2 more minutes.

In a plastic bag, place marinated short ribs, the liquid and the caramelized onions, making sure they're evenly distributed.

Lay flat and seal the bag using a vacuum sealer.

Place the sealed short ribs in the water bath to cook for 24 hours.

Retrieve the short ribs from the water bath and pour the contents into a large bowl. Using your hands or a fork (which you shouldn't even need because it should be super tender!), shred the beef. You may be able to salvage a small bit of the first batch of onions, but they'll mostly be mush.

Cut 1 onion into thin slices and caramelize with sliced mushrooms in butter for 10 minutes. Add sugar and simmer for another 2-3 minutes until golden brown.

Prepare a baking dish with cooking spray and line with the bottom half of the buns.

Place a layer of provolone cheese, a generous layer of shredded beef, a layer of the caramelized onions and mushrooms, and a layer of shredded Gruyere cheese. Top with other half of the bun.

Melt 1 tbsp of butter and mix with 3 tbsp of the liquid from the Sous Vide bag, garlic salt and onion powder.

Brush the top buns with the mixture and sprinkle with fresh thyme.

Bake sliders for 10-15 minutes, or until the cheese is melted. Serve hot!