Asparagus-Cheese Tartines

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Ingredients

1. 12 thin asparagus spears
2. 1 tablespoon extra-virgin olive oil
3. 2 large shallots, thinly sliced
4. Salt and freshly ground pepper
5. 2 large plum tomatoes, sliced lengthwise 1/4 inch thick
6. Four 3/4-inch-thick slices of peasant or Pullman sandwich bread
7. 1/4 cup tapenade
8. Four 1/8-inch-thick slices each of Italian fontina, fresh mozzarella and Gruyère cheese
9. 4 very thin slices of prosciutto
10. Aged balsamic vinegar, for drizzling

1. Bring a large skillet of salted water to a boil. Add the asparagus and cook until crisp-tender, 2 minutes. Drain and transfer to a plate. Wipe out the skillet.
2. Add the oil and shallots to the skillet, season with salt and pepper and cook over moderate heat until softened, 4 minutes. Transfer the shallots to a plate. Add the tomatoes to the skillet, season with salt and pepper and cook over moderately high heat until lightly browned on one side, 2 minutes; transfer to the plate with the shallots.
3. Preheat the broiler. Arrange the bread on a baking sheet; toast in the broiler 3 inches from the heat, turning once, 2 minutes.
4. Spread the toasts with the tapenade and top with the shallots, fontina and mozzarella. Broil the tartines 3 inches from the heat for 1 minute, until the cheese has melted. Top the tartines with the asparagus and drape with the Gruyère. Broil the tartines for 1 minute longer, until the Gruyère has melted. Top the tartines with the tomatoes and prosciutto, drizzle with the vinegar and serve.