Yield: 6 servings.
1 sheet best-quality puff pastry, thawed but chilled
1 pound assorted mushrooms (cremini, oyster, shiitake)
3 tablespoons unsalted butter
1 tablespoon fresh thyme leaves
1 teaspoon salt
½ teaspoon black pepper
1 small sweet onion, peeled, quartered, and sliced
1 tablespoon balsamic glaze 4 ounces Gruyère cheese,
1 pound fresh asparagus, tips only*
Preheat oven to 400 ̊. Gently unfold puff pastry and place in a 10-inch tart or pie pan. Press gently into base and edges. Place pastry in refrigerator until ready to fill.
Clean mushrooms with a damp paper towel. In a skillet, melt butter over medium-high heat. Add mushrooms and thyme, turning to coat. Sauté until mushrooms have released their water, turned golden brown, and are slightly dry. Place mushrooms into a bowl and season with salt and pepper. Set aside.
To the same skillet over medium heat, add onion slices. Cover the pan and cook without touching until onions are soft and have just started to caramelize. Remove from heat.
Drizzle balsamic glaze over the onions. Remove pastry from refrigerator and fill with mushrooms and onions. Sprinkle cheese evenly over mushroom and onion mixture.
Place tart in the oven and bake until puff pastry is golden brown and crisp, about 20 to 25 minutes.
Cool for about 10 minutes. Heat a small skillet on medium-high heat. Add asparagus tips to dry, hot pan, and sauté just until asparagus begins to char. Arrange asparagus tips on tart. Serve warm or at room temperature.
*Chop and save remaining asparagus spears for omelets, pasta, salads, or soups.