Put the butter and the flour in a large mixing bowl and rub together with your fingertips until the mixture looks like grainy sand.
In another bowl, stir together the rest of the ingredients until smooth and runny. Pour over the butter and flour mixture and combine with your hands. When the dough is soft and squidgy, shape it into a ball, wrap it up in cling film and put it in the fridge for 20-30 mins to firm a little.
Just before you remove the dough from the fridge heat your oven to 180C/160C fan/gas 4 and line 2 baking sheets with baking parchment.
Remove the dough from the fridge. Sprinkle some flour on your work surface and on a rolling pin then roll out the dough until it’s about the thickness of a £1 coin.
Use your ruler and a dinner knife to carefully cut the biscuit dough into rectangles that are 10cm long and 3cm wide and put them on the trays, leaving 2 fingers worth of space between each biscuit.
Put the biscuits in the oven for 10-12 mins. Once baked, cool in the trays for a few minutes then carefully transfer to a wire rack until completely cool. Repeat until all the dough is used up.
To decorate, melt the chocolate in the microwave then dip the end of each biscuit in the melted chocolate and leave to set on a plate or tray lined with baking parchment. Before the chocolate sets sprinkle them with a pinch of your favourite toppings then leave somewhere cool for 1-2 hrs. If giving as a gift, pack into little boxes once the chocolate is completely set (keeps for 2-3 days).