Shaved Asparagus, Prosciutto, and Duxelles Tartines | America's Test Kitchen

Ingredients

• 1 pound white or cremini mushrooms, trimmed and quartered
• ¼ cup Madeira or dry sherry
• 3 tablespoons unsalted butter, cut into 3 pieces
• 2 shallots, minced
• 1 teaspoon minced fresh thyme
• ¾ teaspoon table salt, divided
• ½ teaspoon pepper
• ¼ teaspoon sugar
• 1 pound thick asparagus, trimmed and shaved with vegetable peeler lengthwise into ribbons
• 2 teaspoons extra-virgin olive oil
• ¼ teaspoon grated lemon zest plus 1 teaspoon juice
• 4 slices pain de mie, 6 inches wide and ¾ inch thick, toasted
• 4 ounces thinly sliced prosciutto, torn into large pieces