Preheat the oven to 180℃ / 350℉.
Place the sugar and butter in a bowl and mix together with a spoon or rub in with your hands.
50 g caster sugar (superfine sugar), 125 g butter
Rub in the flour and cinnamon and bring the dough together with your hands.
150 g flour, 2 tsp cinnamon
Add the currants and mix through.
55 g currants (or sultanas)
Line a small baking tray with baking paper, and press the dough into the tin. Use a fork to prick the dough.
Bake for 20 to 25 minutes until lightly golden (the cinnamon makes the shortbread darker than usual) and then allow to cool slightly.
Leave to cool for a few minutes, dust with caster sugar, then slice the shortbread into fingers in the tin.
Lift the baking paper and place on a cooling rack to cool completely.