Grease and line two 20cm round, springform cake tins with butter and baking paper. Set aside.

To make the shortbread dough, you can use either a wooden spoon and elbow grease or an electric hand mixer with the beaters attachment. In a large mixing bowl, beat the softened - not melted! - butter until smooth and pale.Add the salt and caster sugar, and vanilla, if using, and cream until well combined and fluffy.

Gradually mix in the all-purpose flour and the rice flour until a shaggy dough forms. Then use your hands to bring the dough together in the bowl, kneading gently if needed, without overworking it.

Divide the dough in half, and working with one half at a time, gently press it into one of the lined tins, all the way into the edges. Use a small handleless mug, glass or a silicone offset spatula, to gently smooth over the top - just enough to remove your fingerprints!

Chill the dough, tins and all, in the fridge for 30 minutes. And preheat the oven to 160C.

Remove the shortbread from the fridge and score - don’t cut! - each round into 8 wedges. Dock each wedge a couple of times with a fork.

Bake the shortbread for 40-45 minutes, swapping the trays around half way through baking for a more even bake. Shortbread baked in a round like this is ready when the edges are a pale golden brown and quite blonde on top still, with no shiny sheen. When removed from the oven, shortbread is still quite soft in the centre, and will firm up as it cools.

Quickly and gently rescore the wedges with a sharp knife, and then allow the Shortbread Petticoat Tails to cool fully before cutting along the scored lines.

Store your shortbread in an airtight container at room temperature for up to one week.