In a bowl add the 4 cups of Guinness Corned Beef and 1 cup of the Guinness Reduction Sauce and gently mix. You want it moist and lightly coated but not super wet. Be sure that the mixture remains warm.
Place the bottom halves of the bun on the baking sheet and bake for 5-6 minutes or until lightly golden brown.
Remove from the oven and evenly divide the meat on the bottom halves of the buns. About 1/4 cup for each bun.
Drizzle some of the remaining Guinness Reduction Sauce over top (you don’t have to use it all). I saved some to dip in as well.
Top the meat with 1 thick slice of cheese.
Place the top half of the bun, cut side up on the pan.
Bake for 5-7 minutes or until the cheese is melted and the top of the bun is toasted.
Remove from the oven, place the top half of the bun on the cheese and place a wooden skewer in it for presentation.