Because they use modernist ingredients, these amounts are given in metric by weight. For more information on how to measure modernist ingredients check out this article.
Mix all of the ingredients together in a small bowl until thoroughly combined.
Salt and pepper the chuck roast then coat with the spice rub, being sure to rub it into the sides. Heat oil in a pressure cooker over medium-high heat. Sear the chuck roast until browned on all sides. This can be done in batches if there isn't enough room in the pressure cooker. Remove the meat from the pressure cooker.
Add oil to the pressure cooker along with the onion and red bell pepper. Cook until softened, about 5 minutes. Add the garlic and cook another 3 minutes. Add the meat back to the pressure cooker, settling it into the onion and pepper mixture. Add enough beef stock and water to begin to cover the beef, about 2" to 3" (50mm to 75mm).
Seal the pressure cooker, bring to full pressure, and cook for 75 to 90 minutes. Remove it from the heat and let it depressurize naturally. Take the meat out of the pressure cooker and shred. Using an immersion blender blend the liquid and vegetables that are left in the pressure cooker. Return the meat to the pressure cooker until ready to serve.
Combine the tangerine juice, chipotle peppers, and thyme in a pot. Bring to a simmer then remove from the heat and let cool for 30 minutes. Add to a blender, puree it, then strain the mixture. Blend the xanthan gum into the puree then pour it all into a whipping siphon. Seal and charge the whipping siphon.
First saute some peppers and onions. Add a spoonful of the beef to a bowl or plate. Garnish with the sauteed peppers and onions then add some of the tangerine-chipotle froth. Sprinkle some thyme leaves on top then serve.