When you only need the yolk, the white can go to waste, so why not turn it into a sweet treat?
Preheat the oven to 140°C (120°C fan/gas mark 1). Add the cream of tartar to the eggs and whisk until the mixture is light and fluffy.
Then slowly add in the sugar and vanilla without whisking too hard to prevent the mixture from flattening.
Bake for 1 hour 30 minutes if you like your meringues crispy, or 1 hour 15 minutes if you prefer a gooey centre.