For the sauce, combine all ingredients then taste: add more hot sauce to your liking.

For the sandwich, heat a large skillet to medium-high heat with the beef and a drizzle of olive oil. Toss around for 5-7 minutes until the edges of the beef start to crisp and darken, then remove from the skillet.

Reduce the skillet heat to medium-low, and add the butter. Swirl the butter in the pan, then place both pieces of bread in the skillet. Top the bread with 1 piece of swiss cheese on either side. On one side of the sandwich, heap the roast beef, sauerkraut, and a drizzle of special sauce. When the swiss cheese starts to melt, bring the two sides of the sandwich together. Flip once or twice in the pan until the cheese is totally melted and the sandwich holds together.

Cut into wedges and serve with extra sauce for dipping if you'd like!