In a small mixing bowl, beat the mascarpone until soft. Add the Kahlua and, once completely mixed through, beat in the sugar. Lay the puff pastry sheet out with a short edge towards you. Spread the tiramisu filling evenly over the sheet.
Use a pizza cutter or sharp knife to cut the pastry into 8 long vertical strips. Grate 20 grams of dark chocolate over the filling. Working with one torsade at a time, take hold of the end furthest from you and fold it down, in half, on top of itself. Transfer to a nonstick or lined baking sheet, twisting it around twice as you lay it down. Gently press the bottom edge closed, then repeat with the rest and chill for 1 hour.
Preheat the oven to 200C / 180C fan. After the pastries have chilled for one hour, lightly brush them with Kahlua and grate over a fine dusting of the remaining chocolate. Bake for 15 minutes until well risen and golden brown. Transfer to a wire rack to cool, or serve warm.