Cook corned beef brisket according to directions. The ways I like to cook are with a slow cooker or braised in a cast iron Dutch oven.
After the brisket is cooked transfer to an oven safe casserole (not needed if cooked in a Dutch oven).
Discard most of the liquid from the cooking method. This water can also be used to cook either the cabbage wedges or potatoes if they are accompanying the meal.
Mix the sugar and mustard together and spread over the top of the brisket. Return to the oven at 400⁰ F. until glaze is slightly browned and bubbly.
Cut the brisket into slices across the grain and serve.
Notes
A suggestion as sides: 1. Fried Cauliflower with Bacon 2. Potatoes with herbs.