Preheat the oven to 325 degrees F. Line 2 baking sheets with parchment paper. Pulse the sugar and 2 tablespoons sesame seeds in a food processor until finely ground.
Transfer the ground sesame mixture to a medium saucepan and add the butter, orange zest and juice, cornstarch and salt. Cook, stirring occasionally, until the mixture comes to a simmer and thickens slightly, about 3 minutes. Transfer to a large bowl; stir in the flour, vanilla and the remaining 2 tablespoons sesame seeds. Refrigerate until cooled and thickened, about 45 minutes.
Drop heaping teaspoonfuls of batter, 4 inches apart, onto the prepared baking sheets. Lightly sprinkle the tops with more sesame seeds. Bake, 1 baking sheet at a time, until golden brown, about 10 minutes. Let cool on the baking sheet until just set enough to lift with a spatula, 1 to 2 minutes, then carefully transfer to a rack. While the cookies are still warm, curl up 2 sides of each cookie with your fingers, then let cool completely. Repeat with the remaining batter (reline the baking sheets between batches).
Photograph by Levi Brown
Courtesy of Food Network Magazine