Burgers with baked portobello mushrooms and blue cheese

Ingredients:

• 4 large portobello mushrooms, stems removed, caps wiped clean
• 3 cloves garlic, finely chopped
• 1/4 tbsp. dry sherry
• 5 tbsp. l. olive oil
• 2.5 tsp coarse salt
• 110 g soft blue cheese at room temperature
• 1 large onion, thinly sliced
• 100 g spinach leaves (about 5 cups)
• 4 burger buns, toasted

Preparation:

1. Place the mushrooms, slice-side up, on a greased baking sheet. Combine the garlic, sherry, 2 tablespoons olive oil, and 2 teaspoons salt in a bowl. Pour the mixture over the mushrooms. Let marinate for at least 30 minutes or up to 2 hours.
2. Preheat oven to 200°C (400°F). Spread the cheese evenly over the mushroom caps. Bake until the mushrooms are tender when pierced with a fork and the cheese is melted, 15-20 minutes. Discard any juices on the baking sheet.
3. Meanwhile, heat the remaining 3 tablespoons olive oil in a large skillet over high heat. Add the onion and cook, stirring frequently, until softened, about 10 minutes. Add the spinach and pan juices. Cook until the spinach wilts. Sprinkle with the remaining 1/2 teaspoon of salt. Arrange the mushrooms on the buns and top with the spinach and onion.