At least 3 1/2 hours before serving, prepare the salt crust in the bowl. of a heavy-duty electric mixer fitted with a paddle, combine the salt and. herbs and mix to blend,add the egg whites and 2/3 cup water, and mix. until thoroughly blended, add 2 cups of the flour, a little at a time, and. knead until the mixture forms a firm, homogeneous dough, 2 to 3 minutes (You may not need all of the flour) The dough should be firm, not too. moist or sticky, or the beef will steam, not roast- if necessary, knead in additional flour or water for a firm dough, Cover with plastic wrap and. let rest at room temperature for a minimum of 2 hours, or up to 24 hours. (This resting period will make the dough less sticky and easier to roll out.). Preheat the oven to 375 degrees F. Prepare the beef: Pat the meat dry with paper towels (Do not salt the. meat at this point, or flavorful juices will be drawn from the meat and it. will not brown evenly) in a large skillet, combine the butter and oil over moderately high heat, when hot, add the beef and sear well on all sides. 2 to 3 minutes per side. Place a salad plate upside down on a large platter,. transfer the seared beef to rest on the salad plate, placing it at an angle. this will allow air to circulate evenly around the beef as it continues to. cook while resting, making for meat that is evenly cooked and tender. let rest for 5 minutes. Meanwhile, on a lightly floured surface, roll the dough out to form a. 10- x 15-inch rectangle, or one large enough to easily enclose the beef. without stretching the dough. In a small bowl, combine the egg yolk and 1/2 teaspoon water to make. a glaze. Set aside. Sprinkle the beef with the thyme. Completely wrap the beef in the salt crust, pressing all the seams together. Be sure that all the seams are well sealed.) Wrap the beef just before roasting. If you wrap it in advance,. the meat and the salt crust will turn soggy.) Transfer the wrapped beef. to a baking sheet. With a brush, coat the entire surface of the crust. with the glaze. Sprinkle the crust with the sea salt. Place the baking sheet in the center of the oven and roast for 15 minutes per pound for rare meat (or until the interior registers 125 degrees F when measured with a meat thermometer). For medium rare, roast an additional. 3 to 4 minutes per pound. The crust should be a light, golden brown. Let. the beef rest in the crust on the baking sheet at room temperature for 1. hour before serving. (The beef will remain warm.). To serve, slice off the crust at one end, remove the beef, and discard. the crust. Season the beef with pepper. Cut on the diagonal into thick. slices and arrange on a warmed serving platter. Serve immediately. Testing for Doneness. There are many ways to test meat for doneness. For beef, insert an instant-. reading meat thermometer into the center of the meat, away from the bones,.and leave it there for 30 seconds. Remove the thermometer to check the interior temperature of the meat: 140 degrees F for rare, 150 degrees F for medium-rare,160 degrees F for medium, 170 degrees F for well done. If you do not have a meat thermometer, do as many chefs do: Place a metal skewer into the thickest part.of the meat and wait 30 seconds. Remove the skewer and touch it to your bottom.lip. If the skewer is cold, the meat is underdone; if the skewer is warm, the meat.is rare; if the skewer is hot, the meat is well done.