Preheat the oven to 150ºC/300ºF/Gas mark 2

Line a baking tray with parchment paper

Flour a shortbread mould with rice flour or semolina making sure the crevices have a good sprinkling

Cream the softened butter, Muscovado sugar and vanilla until the sugar is fully dissolved and there are no lumps

Mix in the flour until just combined, trying not to over-work

Turn out the mixture on to a work surface and form into a ball

put the mixture in the mould and push evenly into all the corners and grooves. Roll a rolling pin over the top a few times to flatten

Turn the mixture out of the mould on to the baking tray

Sprinkle the top evenly with the Demerara sugar

Bake for 30 minutes or until the top is nicely browned

Gently score the top to mark the fingers/petticoat tails

Allow to cool completely on a wire rack

Once cool, cut into pieces ('petticoat' triangles)