Mix balsamic vinegar and honey in small saucepan and place over high heat. Bring to boil, reduce heat to low and simmer until mixture has reduced to 1/4 cup, about 10 minutes. Set aside to cool.
Heat 1 tablespoon olive oil over medium-high in medium skillet. Add red onion slices; sauté until tender. Add remaining tablespoon olive oil, Brussels sprouts and garlic. Season with salt, pepper, rosemary and red pepper flakes. Sauté mixture until sprouts are browned and onions darken. Remove mixture to bowl and set aside.
In skillet onion mixture was cooked in, sear sausage over medium-high until browned. Remove from skillet and set aside. In same skillet, lower cooking temperature to medium and melt butter. Place 1 slice of bread in skillet. Top with half the parmesan, kielbasa sausage and onion and Brussels sprouts mixture. Drizzle some balsamic reduction over top. Layer 3 havarti cheese slices over and top with second slice of bread. Cover skillet and grill until first side is golden brown. Carefully flip sandwich and grill until golden brown. Remove sandwich and repeat steps for second sandwich. Halve sandwiches and serve.
- 1/2 cup balsamic vinegar
- 3 tablespoons honey
- 2 tablespoons olive oil, divided
- 1 cup red onion slices
- 1/4 pound Brussels sprouts, stemmed and quartered
- 3 large garlic cloves, minced
- 1/4 teaspoon salt
- 1/4 teaspoon pepper
- 1/2 teaspoon dried rosemary, crushed
- 1/2 teaspoon red pepper flakes
- 1/3 pound kielbasa sausage, sliced
- 1 tablespoon butter
- 4 thick slices rye bread
- 1 cup (about 3 ounces) Wisconsin Parmesan cheese, grated
- 6 1-ounce slices Wisconsin Havarti cheese