Spread the sliced onions and chopped celery across the bottom of your slow cooker. Generously season the beef short ribs with kosher salt and pepper, then arrange them over the onions and celery.

Distribute the halved shallots, smashed garlic, and chopped carrots around and on top of the ribs.

In a small bowl, whisk together the tomato paste and Worcestershire sauce with a splash of the beef broth until smooth. Pour this mixture, the remaining beef broth, and the red wine over the ingredients in the slow cooker.

Scatter the chopped fresh thyme and add the bay leaf. Secure the lid and cook on LOW for 5-7 hours or on HIGH for 3-5 hours, until the beef is exceptionally tender.

Once tender, carefully remove the short ribs from the slow cooker. If desired, separate the meat from the bones and discard the bones (yields approx. 170-200g cooked meat per serving). Skim and discard any excess fat from the surface of the cooking liquid.

Return the meat to the sauce in the slow cooker. If you prefer a slightly reduced sauce, switch the slow cooker to HIGH and cook uncovered for an additional 20-30 minutes, allowing the sauce to concentrate its flavors.

Preheat your oven to 320°F (160°C).

In a large, oven-safe Dutch oven or braiser, layer the sliced onions and chopped celery on the bottom. Season the beef short ribs liberally with kosher salt and pepper and place them atop the vegetables.

Add the shallots, garlic, and carrots to the pot. In a bowl, combine the tomato paste and Worcestershire sauce with a little beef broth, then pour this, the remaining broth, and all the red wine over the beef and vegetables.

Tuck in the fresh thyme and bay leaf. Cover the pot tightly and transfer to the preheated oven. Braise for 2 to 2.5 hours, or until the short ribs are fork-tender.

Remove the pot from the oven. Carefully take out the short ribs; you can remove the bones at this stage if you wish (yields approx. 170-200g cooked meat per serving). Skim any visible excess fat from the sauce. Return the meat to the sauce.

In a medium skillet over medium-high heat, melt 131​ tablespoons (approx. 19g) of the salted butter. Once shimmering, add the sliced cremini mushrooms in a single layer. Allow them to cook, without stirring, for about 4-5 minutes, or until they achieve a deep golden-brown color on one side.

Add the remaining 131​ tablespoons (approx. 19g) of butter, the chopped fresh sage, and a small pinch of salt and pepper to the skillet. Continue to cook, stirring occasionally, for another 4-5 minutes, until the mushrooms are beautifully caramelized and the butter has a nutty brown hue.