Preheat oven to 350 degrees. Place a very large a very large sheet of aluminum foil over a baking pan. Place the corned beef into a pot of water and bring to a boil. Allow to boil for 1 minute and then remove to waiting paper towels. Pat dry and then place the corned beef, fat side up, on the waiting foil.
Stir together the honey and the mustard. Reserve 2-3 tablespoons in a separate dish and then pour the sauce over the top of the corned beef. Sprinkle the brown sugar evenly over the top. Wrap the beef with the foil, allowing space between the top and sides of the meat and the foil. Bake for 2 hours.
Remove from the oven, change temperature to broil. Open the foil and place back in the oven. Broil for 3-4 minutes, until the top is lightly browned and bubbling. Watch closely while broiling, it will burn very quickly once it has browned! Let the corned beef rest for at least 10 minutes before slicing across the grain of the meat. Serve with the reserved honey mustard sauce. Enjoy!