Toast the guajillo chilis until brittle in an oven, about 10 minutes at 325 F. Cool, break and discard the seeds. Put the dried chili in a bowl, pour over the hot water and rest for 5 minutes.
Combine the soaked chilis and remaining ingredients except the oil in a blender and puree.
Drizzle in the oil at the end to make the sauce smooth, then pour into a container, cool, and refrigerate until needed.
Dry Rub
Mix all ingredients together until thoroughly combined.
Trim and Dry Brine the Brisket
Trim the brisket of excess fat if desired.
Season the briskets all over with salt.
Season the briskets all over with the dry rub using roughly 2 teaspoons per pound of meat, then wrap in cling film and refrigerate overnight.
Smoke the Brisket
Preheat the smoker to 250 F. Smoke the brisket for 3 hours, turning once.
Preheat the oven to 275 F.
Remove the brisket from the smoker and wrap in parchment paper.
Bake the pork brisket in the oven until the meat is fork-tender. I like to put a wide pan of water in the oven to help the meat steam and prevent it from drying out. Expect 2-3 hours for half brisket and slightly longer for a full 4 lb brisket. Allow the brisket to rest in a warm place for 30 minutes before slicing.
Serve the brisket with the mustard sauce and your favorite side dishes like cornbread, mustard or collard greens.
Video
Notes
Leftover brisket is delicious used to make sandwiches or cut into pieces and fried up to make breakfast brisket hash.