Roasted Asparagus and Mushrooms

Name: Roasted Asparagus and Mushrooms
Cook time: 40 min
Total time: 40 min
Cuisine: Eastern European
Ingredients: 1 pound asparagus, trimmed and halved crosswise; 1 pound hen-of-the-woods or oyster mushrooms, or 8 ounces morel mushrooms; 2 tablespoons extra-virgin olive oil; 1 teaspoon kosher salt; 2 tablespoons unsalted butter; 1 tablespoon fresh thyme leaves; 1 cup loosely packed watercress or arugula (about 1/4 ounce); Flaky sea salt (preferably Maldon); Aged balsamic vinegar (preferably San Giacomo Essenza Balsamic), for drizzling