Portobello French Dip

Preheat oven to 200°C.

Slice portobello mushrooms and marinate with olive oil, balsamic vinegar, minced garlic, salt, and pepper for 15 minutes.

Thinly slice onion and caramelize in a pan with olive oil and sugar until golden brown.

Prepare horseradish aioli by mixing mayonnaise, horseradish, and lemon juice in a small bowl. Season with salt and pepper to taste.

Bake the marinated mushrooms on a baking sheet for 15 minutes, or until tender.

Slice the baguette in half and toast lightly.

Layer the caramelized onions, baked mushrooms, and provolone cheese on the bottom half of the baguette.

Place the assembled sandwich under the broiler for 1-2 minutes, or until the cheese is melted and bubbly.

Spread horseradish aioli on the top half of the baguette.

Combine the two halves and serve immediately with extra aioli for dipping.