Preheat oven to 200°F/93°C. Line a baking sheet with parchment paper and set aside.
Make sure that your mixing bowl and the beater is super clean, not greasy and no trace of fat (or egg yolk). In a mixing bowl of an electric mixer fitted with the whisk attachment, combine egg whites, salt and cream of tartar. Beat egg whites on low-medium speed until foamy.
Increase speed to medium high, then slowly add the sugar, one tablespoon at a time, and continue to beat until stiff peaks form. Meringue at this time is thick and shiny, and the sugar is fully dissolved. Add in vanilla extract. Gently fold by hand until combined and smooth. Fold in food coloring at this point if using.
Transfer the meringue to a pastry bag fitted with a large star tip (I use Wilton 1M), pipe 1-inch diameter kisses onto the prepared baking pan lined with parchment paper. You can also spoon mounds of meringue onto the prepared baking sheet, using a tablespoon and flatten the top with the back of the spoon.
Place in the middle part of the oven and bake for 1 hour, or until the meringues are dry and crispy and they are easily lifted from the parchment paper. Turn off the oven and, without opening the door, let meringues cool completely in the oven for at least one hour.
Remove meringue from parchment paper. Store meringue cookies in an airtight container at room temperature.