Here's Chef Mike Bagley's recipe from JB's Sarnie Shoppe.
Ingredients: 2 Roasted Red Skin Potatoes 4 Cabbage Leaves 4 oz. Shaved Corned Beef Marble Rye Bread Sauce Ingredients: 2 oz. Stout ¼ Cup Horseradish 2 Cups Sour Cream 1 Tbsp. Sugar Directions for the Sarnie: 1. Layer thin sliced potato, wilted cabbage leaves and corned beef on Rye bread. 2. Brush the bread with oil and place sandwich in a press. Directions for the Sauce: 1. Whisk together stout, horseradish, sour cream and sugar. 2. Serve on the side with the sarnie.