How to Make It
Melt butter in a small skillet over medium-high. Add panko, crushed red pepper, and 1/8 teaspoon of the salt. Cook, stirring often, until toasted, 2 to 3 minutes. Stir in parsley and tarragon; set aside.
Preheat oven to high broil with rack in middle position. Place asparagus on a rimmed baking sheet, and drizzle with olive oil; toss to coat. Sprinkle with remaining 1/4 teaspoon of the salt, and broil until asparagus is tender-crisp, about 5 minutes (do not stir).
While asparagus broils, place heavy cream in a small skillet. Bring to a gentle simmer over medium, stirring occasionally. Add Parmigiano-Reggiano 1/4 cup at a time, stirring until completely melted and smooth after each addition.
Arrange broiled asparagus on a platter. Spoon cheese sauce over asparagus, and sprinkle with panko mixture and lemon zest.