Bring 8 cups of water to a boil, then add 1/4 cup of salt. Stir to dissolve completely, then add the bay leaf and peppercorns. Remove the brine from the heat, and cool the brine down by transferring it to a bowl that can fit into another bowl filled with an ice bath. While the brine chills, you may trim any visible fat off the pork loin, if you wish. This is a matter of preference. Once the brine has chilled, add the pork loin to the brine and refrigerate for one hour.
Preheat the oven to 375 degrees F, and set a wire rack in a rimmed baking sheet.
Remove the pork loin from the brine and discard the brining liquid. Dry the surface of the pork with a paper towel, then brush the entire surface with the dijon mustard.
Use kitchen twine to pull together and tie the pork loin into as circular of a shape as possible. This will help the pork loin cook evenly (and also look nicer).
Stir to combine both bread crumbs, the rosemary, 1/4 tsp salt and 1/4 tsp pepper, and the olive oil. Press this mixture on the surface of the pork loin, all over the whole loin.
Place the pork loin on top of the wire rack and roast for approximately an hour, but you want to cook the pork loin until a thermometer inserted through the side into the center of the roast reads 138 degrees F. Remove the pork loin from the oven and let it rest for 15 minutes (you may tent it with foil to keep it warm). The resting stage is very important because the residual heat in the pork will further cook it to approximately 145 degrees F, and the juices will be allowed to redistribute. Slice the pork when ready to serve, and enjoy!