The name given to these simple but delicious cookies comes from the method—after placing small balls of dough onto a baking tray, indentations are made with the thumb and then filled with jam.
Preheat the oven to moderate 180°C (350°F/Gas 4). Brush two baking trays with melted butter.
Sift together the flour, bicarbonate of soda and salt. Cream together the butter and icing sugar until smooth and creamy. Add the egg and vanilla and beat well