In a large bowl whisk together the butter, golden caster sugar and light brown sugar.

Add the milk and vanilla extract and whisk again.

Add the Horlicks, flour, flax egg and baking powder and combine before folding through 100g of the dark chocolate chunks. Place in the fridge to chill for 30 minutes.

Preheat oven to 180c and line 3 baking trays with parchment paper.

Evenly divide the cookie dough into 12 and roll the mixture into balls. Place the balls on the baking trays with plenty of space in between.

Flatten slightly and push the remaining chocolate chunks into the tops of each cookie.

Bake in the oven for 15 minutes before allowing to cool and harden slightly before eating.