Preheat the oven to 200°F (95°C). Line 2 baking sheets with parchment paper.
In a clean mixing bowl with a whisk attachment, beat the egg whites on medium low speed until foamy.
When egg whites are foamy, add cream of tartar and salt and continue to whisk.
Then slowly add sugar one tablespoon at a time, while mixer is still running. Allow the sugar to dissolve after each addition.
Gradually increase the speed to medium high and continue beating the egg whites until soft peaks form.
Stir in vanilla extract and continue beating the egg whites until stiff peaks form.
Transfer the meringue into a piping bag with a round tip. (I use Wilton 1A tip.) Pipe 1.5-inch tall mounds on prepared baking sheets. If using candy eyes, place the candy eyes on each meringue.
Bake the meringue cookies for about 2 hours at 200°F. Then turn off the oven and cool the cookies completely in the oven, for a few hours or overnight.
Once completely cooled, transfer the cookies into an airtight container. Store at room temperature for up to 2 weeks