Thaw corned beef brisket in refrigerator for 24 to 48 hours.
Remove brisket from packaging and bring to room temperature on counter over 2 hours.
Pre-heat oven to 275 degrees.
Place corned beef brisket seasoning-side up in 12” cast-iron pan, pour braising liquid in pan, and cover loosely with aluminum foil.
Place pan in middle rack of oven and cook for 6 hours, basting with pan juices every 2 hours.
Remove corned beef brisket from pan and allow to rest for 10 minutes before slicing.
Scrape spices from brisket and slice into 1/2” slices across the grain.
Strain pan drippings and serve on the side with brisket.
Slice Hawaiian sweet rolls in half, slather a teaspoon of mayonnaise on both sides of roll, and toast in a large pan on medium heat until golden brown.