Preheat oven to 250° F and line two large baking sheets with foil or parchment. Stir the cornstarch into the sugar. In a large bowl, beat the egg whites with an electric mixer until soft peaks form. Gradually add the sugar, beating until the mixture holds stiff, glossy peaks, like shaving cream. (If it doesn't get completely stiff, that's OK too.) Beat in the coconut extract, and fold in the coconut. Spread the mixture onto the sheets, about 1/2" thick.

Bake for an hour, then remove from the oven and cool completely. Peel off the foil and break the bark into shards.