For service, the whole beef tenderloin received a hard sear and was finished in a convection oven at 325 degrees with a low fan to finish heating it through. The tenderloin was brushed with whole butter and then sliced. The individual portions were finished with coarse sea salt before serving.
For this dish, Prime CAB (Certified Angus Beef) Tenderloin was served with a sweet onion ash, which gave the beef a slightly sweet and smoky flavor all the way through. The ash mixture was prepared by placing a large dice of yellow onion in a cast iron skillet and leaving it in the 1600 degree broiler for about 1/2 hour, until all moisture was cooked out and nothing remained but cinders. The ash was mixed in a blender with honey powder, dried rosemary, kosher salt, toasted black pepper and Activa RM. Cold water was added to the dry mixture to make a heavy black paste, which was then painted onto the bisected beef tenderloin.
Once one side of both halves received a thorough, but thin coat, the halves were placed back together and the whole tenderloin was wrapped tightly into a cylinder with plastic wrap. The tenderloin was allowed to rest under refrigeration for five hours to allow time for the Activa to bond the proteins. The whole beef tenderloin was cooked sous vide at 137 degrees Fahrenheit for 2.5 hours, then chilled in an ice bath.