Mix the egg whites at room temperature with a pinch of salt on medium high. When it starts to become firm, add the cream of tartar (you can replace it with a teaspoon of apple cider vinegar or a teaspoon of lemon juice) and continue mixing on high speed.
When you get a firm meringue, start adding the sugar gradually, one tablespoon at a time. Mix well after each spoonful of sugar. Add the next spoon of sugar only after the previous one has melted completely. In the end, you should have a nice shiny meringue.
Preheat the oven to 120° C/250° F and line a large baking pan with parchment paper.
Put the meringue into a piping bag and pipe small mounds, about 1½-2 inch diameter, onto the pan. Place the pan in the oven and bake for one hour or one hour 10 mins if you want them nice and firm. Then leave the meringue in the oven with the door ajar to cool.
For the filling, melt the chocolate with the whipping cream in a saucepan over low heat until homogenized. Allow to cool slightly.
Use the chocolate cream to sandwich two meringue pieces together.
These meringue kisses can be kept for up to a week in a cool, dry location.