Place the butter, sugar and flour a bowl and rub together to form a bread crumb mixture. Place bread crumbs onto a baking sheet and near the top of the top oven of the aga for about 5-10 minutes. Make sure you keep checking on it to make sure they don't burn. Remove when the are a golden brown. Leave to cool on the baking tray for a while. If stuck together place in the liquidiser to break it up.