Preheat the oven to 350 degrees F and line a baking sheet with a silicone mat. (You can also use parchment paper.) Beat the butter, sugar, vanilla and salt in a large bowl with a mixer on medium-high speed until light and fluffy, about 3 minutes. Add the egg whites and beat until incorporated. Reduce the mixer speed to low; add the flour and beat until just incorporated. Transfer 1 tablespoon of the batter to a small bowl and stir in the red food coloring.
Spoon 1 tablespoon of the plain batter onto the silcone mat; use an offset spatula to spread the batter into a very thin oval, about 4 by 6 inches. Repeat to make 3 more ovals on the mat. Dip a toothpick into the red batter and drag it diagonally across the ovals to make thin red stripes.
Bake until the cookies are set and the edges are just golden, about 7 minutes. Let cool 45 seconds, then immediately loosen the cookies from the baking sheet with an offset spatula and roll each one lengthwise around a chopstick or the handle of a thin wooden spoon to make a tube. Pull out the chopstick and transfer to a rack to cool completely. (You'll need to work quickly or the cookies will harden; if they do, return to the oven briefly to soften.)
Repeat with the remaining batter, letting the baking sheet cool completely between batches.
Photograph by Andrew Purcell
Recipe courtesy of Food Network Magazine