Mix together the salt, pepper, brown sugar, garlic, rosemary, mustard powder, smoked paprika and chipotle chile powder. Taste and adjust the seasonings.
Clean the ribs with cold water and pat dry. Rub both sides of both ribs evenly.
Then double wrap with foil, making sure to keep track of which side is the bone side. Refrigerate the ribs overnight, the longer the better.
To bake, preheat the oven to 300 degrees and line two baking sheets with foil. Place the foil-wrapped ribs, bone side up, on the sheets, and cook for 1 hour and 30 minutes.
During the last 30 mins they cook stir together the brewed pero, syrup, brown sugar, apple cider vinegar, Worcestershire sauce, garlic, chipotle chile powder and allspice in a saucepan.
Cook over medium until the sugar has dissolved, then whisk in the mustard until well combined.
After the 1 hour and 30 minutes, remove the ribs from the oven.
Gently open the foil (there will be a lot of steam, so be careful) and take 1/4 cup of the meat juices and stir them into the sauce. Adjust seasonings and add salt to taste.
With tongs, remove the ribs from the foil and place back on the sheet (on new foil) meat side up. (Discard the foil that wrapped the ribs, as well as the remaining meat juices).
Brush the meat side of the slabs with the sauce and return to the oven. Cook for 30 minutes uncovered and then brush each slab with the sauce again. Cook for 30 more minutes. Remove from the oven, turn on the broiler, brush each slab with sauce and then cook under the broiler for 1-3 minutes, or until darkened and dark spots appear.
Let the ribs sit about 5 mins, then cut the ribs apart and serve!