In a medium bowl, whisk flour, sugar and salt together.
Add egg whites and vanilla, stir until nice and smooth.
Next, add butter and whisk until combined.
Using a 1 ½ tsp cookie scoop, drop onto prepared baking sheet 4 inches apart.
Carefully place in the oven and bake for approximately 5-7 minutes or until edges start to brown.
Remove from oven, loosen from baking sheet and using a wooden spoon, wrap the cookie around the end of the spoon. Press to seal and hold for 15-20 seconds.
Once set, remove from end of wooden spoon and place of wire rack to cool. Continue with remaining cookies. Let cool completely before filling. *Return to oven for 1 minute if cookies become too cool and unable to shape.