Ingredients:

½ cup butter
½ cup granulated sugar
1 egg
1 teaspoon vanilla
1-2 tbsp milk

1 1/8 cup flour
1 teaspoon baking powder
1 tbsp cocoa powder
½ cup dark chocolate, chopped
1/3 cup milk chocolate, chopped

Method:

Beat the butter and sugar. Add the egg and vanilla.
Combine the flour, salt, baking powder and cocoa in a separate bowl. Add to the butter mixture.
Stir in the milk and chopped chocolate.
Using a teaspoon take some of the mixture, form a small ball and flatten it.
Bake for 10-12 minutes at 180 °C.
Leave to cool and firm up on the tin before removing with a spatula and storing in a cookie jar.