sheet puff pastry (half a 17.3-ounce package), thawed
assorted mushrooms (such as button, cremini, shiitake, and oyster), sliced
kosher salt and black pepper
dry white wine
Gruyère or sharp white Cheddar, grated (1 cup)
white wine vinegar
mixed greens (6 cups)
radishes, thinly sliced
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.