Experimentation always teaches you something. I wanted to play with the salt/spice crust idea to see where it would lead. The crust was easy to build, but would it actually impart its flavor onto the meat sealed inside. What processes would the meat actually undergo.
I reconsidered my first assumption that encasing food in salt was dry heat cooking... is it? The meat inside would actually be steaming in vapors caused by its own juices. Although the salt crust was definitely hardening from dry heat, what was happening under the crust is a different story. After seeing the final result, I felt that the meat would benefit from the spices I chose.
Today was a lamb rack butchering day for me, so I decided to roast a frenched rack for the experiment. Besides, the rib bones protruding upwards from the crust would make an interesting presentation. The salt crust was fortified with generous amounts of fennel seed, peppercorn, dried orange peel, and lavender. Instead of putting liquid into the recipe, I used only egg whites and added them without measurement until the consistency was right.
This is what the crust looked like after baking at 275 for exactly one hour. I let the lamb sit for at least 15 minutes before breaking the rock. The choice of salt doming proved to be an optimum cooking method for lamb rack. The meat was incredibly juicy, and was some of the best I'd ever tasted.
So how did the spices fare with the meat. The inner part of the crust, unlike baking with a pure salt crust, maintained a paste consistency. After cracking the hardened outer layer, the inside just crumbled and peeled away. The assumption here is that the vaporized lamb juices mix with the salt and spices to create a thick flavor paste (or soft crumbly rub) on the surface of the meat. The lamb did pick up some of the spice flavor, although mostly on the surface. It is an interesting note that the spontaneous choice of adding lavender benefitted the lamb more so in an olifactory way than by imparting flavor. The meat was steamed in a cloud of floral vapor.
Given this trial run of the spice crust, my suggestion would be to keep the portions down to an individual size (to have more surface area in touch with the spice). I would also definitely recommend using this technique on lamb rack and highly recommend lavender. If you feel uncomfortable baking under crust without a realistic way to gauge temperature, you can easily stick a digital thermometer probe in the roast and pack the crust around it before baking.