Kosher salt and freshly ground black pepper, to taste
¼cupbalsamic vinegar
Instructions
Preheat oven to 400 degrees F. Line a baking sheet with parchment paper or a silicone baking mat; set aside.
Place puff pastry squares onto prepared baking sheet. Using a fork, pierce each square to create a 1/2-inch border.
Sprinkle Gruyere and Parmesan evenly over the top. Arrange asparagus spears in a single layer over the cheese, alternating ends and tips. Drizzle with olive oil; season with salt and pepper, to taste.
Place into oven and bake until golden brown, about 15-20 minutes.
Meanwhile, to make the balsamic reduction, add balsamic vinegar to a small saucepan over medium heat. Bring to a boil until thick and reduced, about 4-5 minutes.
Serve asparagus tart squares immediately, drizzled with balsamic reduction.