Preheat oven to 350°F and arrange rack to center position.

Bring 6 cups water to a boil in large stock pot.

Take corned beef from packaging, and rinse.

Add meat to boiling water and boil for 10 minutes, remove from water. This step is important to help reduce some of the salty flavor from packaging.

Add olive oil and onion slices to bottom of roasting pan or dutch oven.

Remove corned beef from boiling water and pat dry with paper towels. Place on top of onion slices in roasting pan.

Cut potatoes in half and arrange around corned beef.

Combine the whole grain mustard, spices, brown sugar, and honey.

Evenly spread 3 tablespoons (about half) of the mixture on top of the meat, onions, and potatoes.

Tent the roast pan with foil.

Roast the corned beef until internal temperature reaches 160ºF - which will be about 70-80 minutes.

Carefully remove the pan from the oven and transfer the corned beef to a baking sheet lined with foil.

Switch oven to broil.

Top the corned beef with rest of mustard and brown sugar honey mix, and place under broiler.

Let the top of corned beef glisten under broiler for about 5-8 minutes, until golden brown. Do not let burn.

Remove beef from the oven and allow to rest for 10 minutes on a cutting board.

Make sure to slice against the grain for best texture, and serve hot with potatoes.