How to Make It
Preheat the oven to 400°. Butter 2 large heavy rimless baking sheets. In a medium bowl, mix the sugar and egg whites with a wood spoon until blended. Stir in the flour and melted butter. Drop teaspoonfuls of batter on each baking sheet, spacing them 3 inches apart. Spread them into thin 2-inch rounds using the back of a spoon. Sprinkle each cookie with a tiny pinch of rosemary.
Bake 1 sheet at a time for about 4 to 6 minutes, or until the cookies are gold around the edges. Using a metal spatula, quickly transfer the cookies to a rack to cool. If any harden on the baking sheet, return the sheet to the oven for about 1 minute to soften them. Wipe off the baking sheet and butter it again between batches.