Drain sauerkraut well by pressing in a sieve or clean towel until most liquid is removed. Heat 1 tsp vegetable oil in a small skillet over medium heat. Add drained sauerkraut, caraway seeds (if using), and black pepper. Sauté, stirring, 2–3 minutes until warmed through and slightly softened. Remove from heat and set aside.

Prepare Meats

Heat corned beef and sausage

In a separate skillet over medium heat, add the sliced homemade spicy sausage and warm 1–2 minutes per side until lightly browned. Push sausage to the side of the pan and add the thinly sliced corned beef in a single layer (or folded if thicker). Heat corned beef 1–2 minutes until just warmed through — avoid overcooking to keep it tender. Remove both from heat and tent with foil to keep warm.

Assemble meat stack

On a cutting board, layer the warmed corned beef, sausage slices, and pepperoni to create the sandwich filling.

Assemble and Grill Sandwich

Spread 1 tsp Dijon mustard on the inside of one rye slice. Top with 1 slice Swiss cheese, then place the layered corned beef, sausage, and pepperoni. Spoon the warmed sauerkraut evenly over the meat, then add the second slice of Swiss cheese and place the second slice of rye over all, mustard side down.

Butter the outer faces of both rye slices with about 1/2 tbs butter each (total 1 tbs). Heat a clean skillet or griddle over medium-low heat. Place the sandwich in the skillet and press gently with a spatula or a heavy pan. Grill for 3–4 minutes per side, or until bread is golden brown, buttered, and cheese is melted. If the bread is browning too quickly before cheese melts, lower heat and cover the pan for a minute to trap heat.

Remove sandwich to a cutting board, let rest 1 minute, then slice in half and serve immediately.