Get lucky with the Irish Burger. Topped with Corned Beef, Guinness mustard, Swiss cheese, and onions. Totally awesome!
Mix mustard ingredients into a small bowl. Optionally, add additional sugar or Guinness to flavor. Cover & set in fridge. You can do this up to a day ahead of time.
Cut onion in half and thinly slice.
Form four 1/4 pound burgers in the shape of the bread you're using.
Toast bread in toaster or with butter in a pan. Spread mustard on each piece of toast (so both top/bottom of the insides are coated).
Salt & pepper both sides of the patties and then cook on pan or grill. Flip & add cheese. Cook until done (140F for medium) - usually about 3-5 min a side on a grill or 1.5 min on a pan.
Place burger on a slice of bread. Top with sliced onions & corned beef. Enjoy!