Preheat your oven as low at it will go, ideally 212°F (100°C ) or less and line two baking trays with non stick baking paper.
Beat egg whites in a bowl using hand mixer or stand mixer until it starts to form stiff opaque white peaks
Slowly add sugar, a table spoon or two at a time, make sure sugar is well beaten in in between adding more sugar.
Add the salt, vanilla and vinegar and mix in well
Add mix to a clean pipping bag fitted with a fluted nozzle.
Pipe on to tray in small circles about 2 inches (5cm) diameter, spaced about 1 inch (2.5cm) apart.
Sprinkle with rainbow coloured sprinkles (optional)
Bake in oven for 1.5 hours or until crisp and hollow sounding when tapped.
Turn off oven and allow to cool completely.
Eat immediately or store in a air tight container for up to a week
Delicious on their own or served with ice cream, fresh cream or fresh fruit!