Place the egg whites in the bowl of a stand mixer and beat on high until stiff peaks form. Gradually add the caster sugar, 1 tablespoon at a time, beating for 30 seconds in between.
Once all of the sugar has been added, beat for a further 6 to 8 minutes or until the egg whites have become glossy and thick.
Preheat your barbecue for low and slow cooking (please refer to your handbook for further instructions).
Add the white vinegar and vanilla to the egg whites and beat until combined.
Line a baking tray with baking paper. Using a teaspoon drag three lines of the caramel into a piping bag fitted with an open star piping nozzle. Fill the piping bag with the meringue, and pipe 5cm rounds onto the baking paper, allowing room to spread. Sprinkle the meringues with the sea salt.
Once the barbecue is preheated, make adjustments to the burner control(s) if required (please refer to your handbook for further instructions). Place the tray of salted caramel meringues on the barbecue and low and slow bake for 35 to 40 minutes or until crisp to the touch. You may need to make small adjustments to the far right burner to try and achieve a slightly higher temperature between 130° to 140°C.
Once cooked, turn the barbecue off and allow the meringues to cool in the barbecue for at least 30 minutes.