Preheat the oven to 350 degrees F and line a mini baking sheet with parchment paper or a silicone liner. Set aside.
Beat egg white and cream of tartar with an electric mixer on high speed until foamy.
Add the sugar very slowly, about 1 tablespoon at a time while still beating.
Add the vanilla extract and continue beating until the meringue is shiny. Mixture should have stiff peaks and sugar should be completely dissolved.
Meringues may be dropped by the tablespoonful onto the lined baking sheets or piped onto the sheets using a pastry bag, leaving a 1-inch space between each cookie.
Place the baking sheet in the preheated oven and turn the oven off.
Leave the cookies undisturbed in the oven for 2 hours.
Remove from the oven to cool.
Notes
Expert Tips
Be careful not to leave any of the egg yolk with the egg white. This will interfere with the egg whites foaming.
If your egg whites have been kept in the refrigerator, bring them to room temperature. Warmer eggs whip faster than cold eggs
Use glass, copper or stainless steel bowls when making meringues. Plastic bowls can sometimes harbor traces of grease which will prevent the egg whites from getting stiff.
Use super-fine sugar when making meringues because it dissolves faster than regular sugar and gradually add the sugar, a tiny bit at a time while beating continuously.
Try not to over-whip the egg whites. The meringue should be shiny and glossy so stop whipping when stiff peaks form.
If possible, try to avoid making meringues on humid or rainy days. This could affect how the meringue cookies turn out. If necessary, you might need to increase the baking time.