Step 1

Place corned beef with fat side down into a large slow cooker and pour enough water over corned beef to cover. Cook on High until beef is tender, about 3 hours.

Step 2

Place potatoes into a large pot, cover with water, and stir in salt to taste; bring to a boil. Reduce heat to medium-low and simmer until tender, about 20 minutes. Drain.

Step 3

Place a steamer insert into a saucepan and fill with water to just below the bottom of the steamer. Bring water to a boil. Add cabbage, cover, and steam until tender, 8 to 10 minutes.

Step 4

Melt butter in a saucepan and stir honey and horseradish mustard into butter. Bring to a boil and remove from heat.

Step 5

Set oven rack about 6 inches from the heat source and preheat the oven's broiler.

Step 6

Place corned beef, fat side down, into a roasting pan. Pour half the honey-mustard sauce over brisket; broil until corned beef is golden brown, about 5 minutes. Serve corned beef with boiled potatoes and cabbage, topped with remaining honey-mustard sauce.