Preheat the oven to 180°C / 160°C fan and line two flat trays with baking paper.
Put the room-temperature butter into a mixing bowl and use a wooden spoon or spatula to mix in the sugar, until smooth.
Add the egg and mix until combined then tip in the flour and 160 grams of the chocolate chunks, and stir until just mixed through.
Space out 12 tablespoon-sized amounts of the mixture on each prepared tray, and stick a few reserved chocolate chunks on top of each.
Bake for 12 minutes, turning once halfway through. Leave to cool for 10 minutes on the baking tray then move them to a wire rack.
Baileys Hot Chocolate
Put the milk, double cream, Baileys and sugar into a saucepan and gently bring to the boil. Switch off the heat then tip in the finely chopped chocolate and whisk until you have a smooth, velvety hot chocolate.
Put a scoop of ice cream into a coupe glass. Pour over the hot chocolate and serve with a biscuit on the side.