Preheat your oven to 300°F
Trace an 8 inch circle on a piece of parchment and set upside down on a baking sheet (SEE NOTES)
Separate the egg whites, making sure not a drop of yolk remains
Weigh the whites to make sure you have 150 grams of liquid
Weigh your sugar to make sure you have 250 grams and grind it in a food processor or coffee grinder and set aside
Make sure your mixing bowl is well washed and dried and before starting to mix rub the ½ lemon all over it (SEE NOTES)
Whip your egg whites, salt and cream of tartar until you get medium stiff peaks
Start adding in the sugar slowly, 1 tbsp at a time, till you get stiff peaks (SEE NOTES)
Make a slurry of the vinegar, vanilla and cornstarch and gently fold in
Transfer your mixture to the parchment, staying inside the 8 inch circle you drew, making a dome with a flattened top.
Reduce the heat to 225° and bake for 90 minutes (SEE NOTES)
Once the Pavlova is done, DO NOT remove it from the oven. Leave it in the oven with a light on for 6 hours so it cools down gradually.
After 6 hours, remove it carefully and if it still seems warm leave it outside in a dry place where it will not be disturbed till it is totally cool (SEE NOTES)