- 4 (3-inch-wide) portabella mushroom caps, stems discarded
- 2 plum tomatoes, halved lengthwise
- 3 tablespoons olive oil
- 1/2 teaspoon salt
- 1/4 teaspoon black pepper
- 1 teaspoon distilled white vinegar
- 4 large eggs
- 1/2 teaspoon balsamic vinegar
- 4 thin slices Fontina cheese
- 1 tablespoon finely chopped fresh chives
- Preheat broiler.
- Brush mushrooms and tomatoes with oil and sprinkle with salt and pepper. Arrange mushrooms, stemmed sides down, and tomato halves, cut sides up, on a broiler pan.
- Broil vegetables about 6 inches from heat, turning over mushrooms halfway through cooking, until tender and tomatoes are slightly charred, about 7 minutes total. (Leave broiler on.)
- While vegetables are broiling, fill a deep 10-inch skillet with 1 1/4 inches cold water. Add white vinegar and bring to a simmer.
- Break 1 egg into a cup, then slide egg into simmering water. Repeat with remaining eggs, spacing them in skillet, and poach at a bare simmer until whites are firm but yolks are still runny, 2 to 3 minutes.
- Gently transfer eggs with a slotted spoon to paper towels to drain and season with salt and pepper.
- Sprinkle stemmed sides of mushrooms with balsamic vinegar, then put 1 tomato half, cut side up, on each mushroom and top with an egg. Cover eggs with cheese slices and broil until cheese is just melted, about 1 minute. Sprinkle with chives and serve immediately.