2) In a medium bowl, sift together the flour and salt, then add them to the butter-sugar mixture. Mix on low speed until the dough starts to come together.
3) Dump the dough onto a surface dusted with flour and shape into a flat disk. Wrap in cling film and chill for 30 minutes.
4) Roll the dough 1cm thick and cut biscuits with a 7.5cm by 2.5cm finger-shaped cutter. Place the biscuits on an ungreased baking sheet and sprinkle with sugar.
5) Bake for 20 to 25 minutes, until the edges begin to brown. Allow to cool to room temperature. When the biscuits are cool, place them on a baking sheet lined with greaseproof paper.
6) Put 75g of the chocolate in a glass bowl and microwave on high power for 30 seconds. (Don't trust the microwave timer; time it with your watch.) Stir with a wooden spoon. Continue to heat and stir in 30 second increments until the chocolate is just melted.
7) Add the remaining chocolate and allow it to sit at room temperature, stirring often, until it's completely smooth. Stir vigorously until the chocolate is smooth and slightly cooled; stirring makes it glossier.
8) Drizzle 1/2 of each length of biscuit with just enough chocolate to coat it. Allow the chocolate to cool and harden before serving.