Put butter, sugar and treacle into saucepan, very slowly bring to the boil, stirring all the time.
1 teaspoon bicarbonate of soda, 1 tablespoon milk
Remove from heat. Add bicarbonate of soda dissolved in milk.
Pour hot mixture on to dry ingredients. Mix thoroughly. Leave on one side for 30 minutes or until firm.
Break off 18 pieces of mixture and roll into walnut sized balls.
Transfer to buttered baking trays (leaving room between to allow for spreading), Bake in centre of moderate oven 170C for 10 -12 minutes.
Leave on trays for 1 or 2 minutes before transferring to wire cooling rack. Store in an airtight tin when cold.
Notes
Do watch your oven temperature, as ovens can be slightly different and the high sugar content means that these cookies may burn around the edges if the oven is too hot.