- 1 sheet puff pastry (half a 17.3-ounce package), thawed
- 4 tablespoons olive oil
- 10 ounces assorted mushrooms (such as button, cremini, shiitake, and oyster), sliced
- 1 shallot, sliced
- kosher salt and black pepper
- 1/4 cup dry white wine
- 4 ounces Gruyère or sharp white Cheddar, grated (1 cup)
- 1 teaspoon Dijon mustard
- 1 teaspoon white wine vinegar
- 4 ounces mixed greens (6 cups)
- 2 radishes, thinly sliced
- 1 tablespoon chopped fresh chives
- Heat oven to 400° F. Unfold the pastry and cut it into 4 squares. Place the squares on a parchment-lined baking sheet and, using a fork, prick the dough all over.
- Meanwhile, heat 2 tablespoons of the oil in a large skillet over medium-high heat. Add the mushrooms and shallot and season with ½ teaspoon salt and ¼ teaspoon pepper. Cook, tossing occasionally, until the mushrooms are browned and tender, 4 to 5 minutes. Add the wine and cook until nearly evaporated, about 1 minute more.
- Dividing evenly, sprinkle the pastry squares with half the cheese, leaving a ½-inch border on each. Top with the mushroom mixture and remaining cheese. Bake until the pastry is golden brown, 20 to 25 minutes.
- In a large bowl, whisk together the mustard, vinegar, the remaining 2 tablespoons of oil, and ¼ teaspoon each salt and pepper. Add the greens and radishes and toss to coat. Serve the tarts with the salad and sprinkle with the chives.