1. Preheat the oven to 180C. Line two large baking trays with baking paper. (See Note)
2. If you need to make your own icing sugar, add sugar (75g) to the bowl and grind Speed 9 / 10 seconds. Set aside in a small bowl.
3. Add the butter (220g) to the bowl. Mix Speed 5 / 40 seconds. Scrape down sides.
4. Add the plain flour (200g), icing sugar (75g), cornflour (50g), milk (60g) and vanilla extract (1/2 tsp) to the bowl. Mix Speed 6 / 30 seconds. While mixing, check through the lid to see how thick the mixture is. If it appears too thick (i.e., it is not creaming together at all but is crumbly instead), add a little more milk until you have a very thick, almost buttercream-like texture.
5. Fill the mixture into a piping bag with a very large star nozzle (make sure it is super large, otherwise the piping will be difficult).
6. Pipe little S shapes onto the prepared baking trays, leaving a 3cm gap in between each biscuit.
7. Bake in the oven for 10-12 minutes until pale and still a little soft. Remove and leave to cool on a wire cooling rack.

Topping:

1. Meanwhile, add the dark chocolate pieces (200g) to the bowl. Blitz Speed 9 / 7 seconds. Scrape down sides.
2. Program 4 minutes / 37C / Speed 2. Check after 2 minutes to see if the chocolate has already melted. Depending on the amount of cocoa in the chocolate, it may melt faster than 4 minutes.
3. Pour into a small bowl and dip each biscuit into the chocolate.
4. Place back on the baking trays and leave to harden. These biscuits store well up to 2 weeks.
5. Enjoy!

Note: If you have a fan oven, these biscuits are very likely to fall apart a little and become a flatter because the fan (at 160C) will be quite hot and create steam rather than "drying them out" by using a non fan setting. It is best to use the non fan setting of the oven (at 180C) or to place the trays in the fridge for 30 minutes before baking.