Dunder Recipe

In a small bowl combine prepared horseradish, sour cream, mayonnaise, lemon juice, Dijon, Worcestershire, salt and pepper. Stir until smooth. Taste and adjust horseradish or salt as desired. Refrigerate until assembly.

Heat 1 tablespoon olive oil and 1 teaspoon butter in a medium skillet over medium heat until shimmering.

Add the thinly sliced onion, sprinkle with 1/4 teaspoon salt and 1/8 teaspoon black pepper. Cook, stirring occasionally, until onions are soft and golden brown, about 10–12 minutes. Reduce heat if they begin to brown too quickly.

When soft and caramelized to your liking, remove from heat and set aside.

In a small saucepan combine 1 cup beef broth, 1 teaspoon soy sauce, 1/2 teaspoon Worcestershire sauce and 1/2 teaspoon minced garlic. Bring to a gentle simmer over medium heat.

Whisk together 1/2 teaspoon cornstarch and 1 tablespoon cold water until smooth. Slowly whisk the slurry into the simmering broth to lightly thicken. Simmer 1–2 minutes until slightly glossy. Stir in 1 teaspoon butter and season with a few grinds of black pepper. Keep warm over the lowest heat.

Preheat a skillet or griddle over medium heat.

Butter one side of each slice of potato bread (use the 2 tablespoons butter apportioned for the sandwich). Place one slice, buttered side down, on the skillet.

Layer on one slice Havarti and one slice Gouda. Pile half of the shaved prime rib evenly over the cheese. Spoon half of the sautéed onions over the meat, then dot or spread about half of the horseradish cream sauce on top (reserve remaining sauce for serving). Add the second slice of Havarti and Gouda if you prefer extra cheese, or proceed with the second bread slice, buttered side up.

Place the second slice of potato bread on top, buttered side up, and cook until the bottom is golden and the cheese begins to melt, about 2–3 minutes. Carefully flip and cook the other side 2–3 minutes more, pressing lightly with a spatula so the sandwich holds together and the fillings warm through.

Transfer sandwich to a cutting board, let rest 1 minute, then cut in half.

Serve the sandwich with the warm au jus in a small bowl for dipping and the remaining horseradish cream sauce either spread alongside or dolloped on top. Sprinkle a light pinch of kosher salt and optional chopped parsley over the sandwich halves.