Position an oven rack in the center of the oven and preheat to 325 degrees F.
In a bowl stir the salt and water together and add flour for some extra binding. Froth up the egg whites with a fork, add to the salt and flour and blend until the mixture forms a stiff paste resembling wet snow while holding its shape when you squeeze it together.
Spread the mixture to form a salt bed in the bottom of a large roasting pan, and lay the roast on top, fat-side down. Cover it all over with the rosemary, thyme and cracked black peppercorns, pressing into the roast to make sure it adheres well. Coat it completely with the salt dough, patting it well so that when it roasts it will solidify into a solid casing. It needs to be about 1/4-inch thick.
Roast the beef for 20 minutes per pound for medium-rare.
Transfer the beef to a cutting board, let it rest for 15 minutes and then, cut the casing open and slice in between the bones for nice manly servings. You can also remove the bones and slice thinner if you want.