Preheat the oven: Preheat your oven to 300°F (150°C). Line a baking sheet with parchment paper and draw a 5-inch (13 cm) circle on the paper as a guide.
Whisk the egg whites: In a clean, dry bowl, beat the egg whites on medium speed until they become frothy. Add the cream of tartar and continue to beat until soft peaks form.
Add sugar: Gradually add the sugar, one tablespoon at a time, while continuing to beat the mixture. Beat on high speed until stiff, glossy peaks form, and the sugar is fully dissolved.
Add remaining ingredients: Gently fold in the vanilla extract and white vinegar using a spatula.
Shape the meringue: Spoon the meringue onto the prepared baking sheet, using the circle as a guide. Shape it into a disk with slightly raised edges to hold the toppings.
Bake: Place the meringue in the oven and immediately reduce the temperature to 250°F (120°C). Bake for 45 minutes to 1 hour, or until the meringue is crisp and dry on the outside. Turn off the oven, leaving the meringue inside to cool completely.
To make the custard:
Mix egg yolks and sugar: In a medium bowl, whisk together the egg yolks and sugar until well combined and slightly thickened.
Heat the milk: In a medium saucepan, heat the whole milk over medium heat until it just begins to simmer. Do not let it boil.
Temper the egg mixture: Slowly pour about 1/4 cup of the hot milk into the egg yolk mixture, whisking constantly to temper the eggs. Gradually add the tempered egg mixture back into the saucepan with the remaining milk.
Cook the custard: Continue to cook the mixture over medium-low heat, whisking constantly, until it thickens slightly and coats the back of a spoon, about 8-10 minutes.
Add vanilla: Remove the saucepan from the heat and stir in the vanilla extract.
Cool the custard: Pour the custard into a bowl and cover the surface with plastic wrap to prevent a skin from forming. Let it cool to room temperature, then refrigerate for at least 1 hour before serving.
To assemble:
Once the meringue has cooled, gently lift it off the parchment paper and place it on a serving plate.