1. Cover the tomahawk steak generously in a tex-mex steak rub.
2. Insert a waterproof, wireless thermometer into the thickest part of the steak.
3. Place the seasoned steak in a ziplock bag or vacuum-sealed bag, ensuring it's completely sealed.
4. Place the bagged steak in a dishwasher on a hot cycle (without soap) or into a sous vide controlled container of water set to your desired temperature for medium-rare (e.g., 130-135°F / 54-57°C).
5. While the steak is cooking, prepare the Tex-Mex chimichurri: Combine 1 cup cilantro, 1/2 cup chopped parsley, 3 minced cloves garlic, 1 minced jalapeno, 4 tbsp red onion, 3 tbsp spicy vinegar, 1 tbsp lime juice, 1.5 tsp tex-mex rub, and 1/3 cup olive oil. Mix well and set aside.
6. Once the steak hits an internal temperature of 135°F (57°C), carefully remove it from the dishwasher/sous vide and dry it thoroughly with paper towels. At this point, the steak should be evenly cooked throughout with rendered fat.
7. Heat a cast iron skillet or heavy pan to at least 400°F (200°C) over high heat. Add beef tallow to the hot pan.
8. Sear each side of the steak for 1-2 minutes until a deep brown crust develops.
9. Remove the steak from the pan, let it rest for a few minutes, then cut it against the grain.
10. Top the sliced steak with the Tex-Mex chimichurri and season with salt and pepper to taste before serving.
