I've just done a wee internet search and found out you can buy it from Ocado! Well I never...
225g Butter (room temp)
285g Plain flour
4 tbsps sugar
1 egg for glazing
Mixed chopped nuts
Pre-heat the oven to 175 degrees C.
Rub the butter into the flour until it resembles breadcrumbs, then add the sugar and bring the whole thing together into a dough. Don't knead it!
Let it rest in a polythene bag or clingfilm in the fridge for half an hour or so, then roll it out into finger-thick sausages and cut pieces about the size of your thumb, diagonally.
Put them on a baking tray and press each one gently with a fork. Beat an egg with a little water and brush each biscuit with it. Mix an equal amount of parl socker and nuts, and sprinkle them on top. Bake in the oven for 12-15 minutes & cool on a wire cooling rack.