This recipe works best with 1/2-inch-thick spears. Work quickly when tossing the asparagus with the egg whites, as the salt will rapidly begin to deflate the whites.
1. Adjust oven rack to middle position and heat oven to 450 degrees. Line rimmed baking sheet with aluminum foil and spray with vegetable oil spray. Using fork, poke holes all over asparagus. Toss asparagus with 1/2 teaspoon salt and let stand for 30 minutes on paper towel–lined baking sheet.
2. Meanwhile, combine 1 cup Parmesan, panko, melted butter, 1/4 teaspoon salt, 1/8 teaspoon pepper, and cayenne in bowl. Transfer half of Parmesan mixture to shallow dish and reserve remaining mixture. Using stand mixer fitted with whisk, whip egg whites with honey on medium-low speed until foamy, about 1 minute. Increase speed to medium-high and whip until soft peaks form, 2 to 3 minutes. Pour egg white mixture into 13-by-9-inch baking dish and toss asparagus with egg white mixture. Working with 1 spear at a time, dredge half of asparagus in Parmesan mixture and transfer to baking sheet. Refill shallow dish with reserved Parmesan mixture and repeat with remaining half of asparagus.
3. Bake asparagus until just beginning to brown, 6 to 8 minutes. Sprinkle with remaining 1/2 cup Parmesan and continue to bake until cheese is melted and panko is golden brown, 6 to 8 minutes longer. Transfer to platter. Serve.
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"Vegetables are perishable, so we don't have any indication of what they looked like 500 years ago," says James Nienhuis, a professor in the Department of Horticulture at the University of Wisconsin.