Preheat your oven to 180°C and line a baking tray with baking paper.
Using a freestanding mixer or electric beater, beat the butter until smooth. Add the castor sugar and cream together until pale and fluffy. Mix in the vanilla extract.
Sift in the flour and salt. Add the ground almonds and then beat until the mixture comes together.
Take one half of the dough out of the mixing bowl and gently knead with your hands for a minute to help bring it together. Set to one side. Sift the cocoa into the mixing bowl, over the other half of the dough. Beat in, then knead with your hands until the cocoa is fully incorporated.
Roll the vanilla dough into a sausage with a diameter of about 3cm. Do the same with the chocolate dough. Then, gently press the two rolls together, then roll them into a combined sausage that is about 30cm long / has a diameter of 3-4cm. (Yoh, we're getting technical here!)
Cut the roll into 1cm slices and arrange these on your prepared baking tray. Bake for 15 minutes or until lightly golden at the bottom. Transfer to a cooling rack to cool completely.
Melt the dark chocolate chips and pipe or drizzle over the cooled biscuits. Leave to stand for a few minutes so that the chocolate can set, then serve.