Prepare the Ingredients: Start by slicing the onions, mincing the garlic, and chopping the bacon into small pieces. Slice the cremini mushrooms and set aside. Cut the chuck roast into bite-sized chunks and season generously with salt and black pepper. Rub the Dijon mustard evenly over the meat.
Sear the Meat: Heat a large skillet or the Instant Pot on the sauté setting. Add a bit of oil and sear the seasoned meat in batches until browned on all sides. This step adds depth of flavor to the dish by caramelizing the meat.
Sauté the Aromatics: In the same skillet or Instant Pot, add the bacon and cook until it begins to render its fat. Then, add the onions and garlic, cooking until softened and fragrant.
Combine Ingredients: Transfer the seared meat, onions, garlic, and bacon to the Instant Pot or slow cooker. Add the sliced mushrooms, bay leaves, Maggi seasoning, tomato paste, and beef stock.
Add the Beer: Pour the double bock beer over the meat and vegetables, ensuring they are fully submerged in the liquid.
Cook: If using an Instant Pot, seal the lid and set to manual high pressure for 60 minutes. For a slow cooker, cook on low heat for 6-8 hours or until the meat is tender and falling apart.
Adjust Seasoning: Once the cooking time is complete, taste the Bierfleisch and adjust the seasoning as needed with salt and pepper.
Serve: Serve the Bavarian Bierfleisch hot, garnished with fresh herbs if desired. Enjoy alongside your favorite sides such as mashed potatoes, spaetzle, or crusty bread.