From The National Trust Complete Recipe Book.
175g (6 oz) soft butter
85g (3 oz) icing sugar
175g (6 oz) plain flour
55g (2 oz) custard powder
1. Cream the butter and sugar together very thoroughly until light and fluffy. Add the flour and custard powder and mix to form a firm dough. Break off small pieces, the size of a walnut, and roll into a ball with your hands.
2. Place on the cold plain shelf lined with Bake-O-Glide. Flatten slightly and mark the holes of a ‘button’ in the centre of each biscuit.
3. Slide the plain shelf onto the third set of runners in the baking oven. Cook for 10-15 minutes until lightly golden.
AGA R5 Series 2-Oven: Slide the baking tray onto the oven grid shelf set on the floor of the roasting oven with the cold plain shelf above, on the second runners down. Cook for about 10-12 minutes until lightly golden.
Rayburn and Conventional Cooking: Main Oven set at 180°C, 350°F or Gas Mark 4. Cook in the centre of the Main Oven for 10-15 minutes until lightly golden.
Cool on a wire rack.