8 large caps (about 2 pounds) portobello mushrooms
1/2 cup pastrami seasoning*
1/4 cup olive oil
8 slices dark rye bread
1/2 cup Thousand Island dressing
2 cups (1 pound) sauerkraut
8 1-ounce slices Gruyère Cheese
4 ounces (1 stick) butter, softened
Place clean mushroom caps upside down on sheet pan and liberally sprinkle with pastrami seasoning mixture. Cover and let mushrooms stand for several hours, to marinate.
In large skillet, heat oil; add mushrooms and sauté evenly on both sides for 6 minutes or until softened and lightly browned. Remove from heat and cool. Slice and reserve.
Place bread slices on clean, flat surface, lay out the bread slices. Spread each slice with dressing. Top 4 slices of bread with the sauerkraut and sliced mushrooms. Lay cheese slices over tops of the mushrooms, and top with remaining slices of bread.
Spread the sandwiches with softened butter and cook in a nonstick skillet until golden and the cheese has melted. Serve immediately.
*If unable to find pastrami seasoning, combine 3 tablespoons each garlic powder and brown sugar. Add 1 tablespoon cracked black pepper, 1 teaspoon ground allspice, 1/2 teaspoon ground cloves, 1 teaspoon ground coriander, and 1/2 teaspoon salt. Mix well.