Just recalled I have shortbread moulds, five in all, one is well used from my late MIL, a fantastic baker. Two have thistle pattern. Ashamed, as a Scot, to admit I've never used them!
MIL's recipe is 6 oz flour, 2 oz rice flour or cornflour, 2 oz castor sugar, 4 oz butter and pinch of salt.
Mix the dry ingredients.
Add butter in a piece and work in till right consistency (not sure what this is!)
Turn onto board and cut into shapes about 3/4" thick. Prick tops.
Bake in steady oven till they begin to colour, then moderate oven and bake slowly about 1 hr.
Leave in oven to cool.
MIL was professional head cook in big country houses, and her instructions are rather vague but her shortbread was to die for!!