1. Heat your oven to 160C fan-forced (180C conventional). Place the butter and sugar in the bowl of a stand mixer and mix at high speed for about 5 minutes, until pale and fluffy. Add the eggwhites and vanilla and mix for a further 5 minutes until completely combined. Reduce the speed of the mixer to very low and add the salt, then the flour, a third at a time until it is all combined. Transfer the mixture to a piping bag with a 1cm-round nozzle. 

2. Pipe 8cm lines onto a lined baking tray, leaving about 5cm between each line to allow the biscuits to spread. Sprinkle a tiny pinch more flake salt on top of the batter and bake for 12-15 minutes, until the biscuits start to brown around the edges. Allow to cool on the tray for 5 minutes until firm enough to transfer to a wire rack to cool completely. Serve with coffee.

Also try Adam Liaw's Filipino pork skewers