This exceptional sandwich originated at Penny Cluse Cafe in Burlington, Vermont. The spinach, mushroom and onion filling is so satisfying, you won't even miss the corned beef. Recipe courtesy EatingWell.com
Prepare Russian dressing: Whisk mayonnaise and ketchup in a small bowl until smooth. Stir in capers and pickle (or relish).
To prepare sandwiches: Heat 2 teaspoons oil in a large nonstick skillet over medium-high heat. Add onion and mushrooms; cook, stirring often, until the onion is softened, 4 minutes. Add spinach and cook, stirring, until it has wilted, 1 to 2 minutes. Transfer the mixture to a plate.
Coat the pan with the remaining 1 teaspoon oil and return to medium heat. Add the bread; divide cheese equally among the slices. Divide sauerkraut between 2 slices and divide the spinach mixture between the other 2 slices; cook until the cheese has melted and the bread is golden brown, 4 to 6 minutes. Transfer sandwich halves to a cutting board. Divide the dressing between the spinach halves. Carefully place the sauerkraut halves on top. Cut sandwiches in half and serve.