1. If you need to make your own caster sugar, add sugar (60g) and grind Speed 9 / 3 seconds.
2. To make the dough, place the milk (100g only), yeast (2 Tbsp) and caster sugar (60g) in the bowl. Program 2 minutes / 37C / Speed 2.
3. Add the flour (500g), butter (30g only), salt (1.5 tsp) and remaining milk (200g) to the bowl. Program 2 minutes / Closed Lid / Kneading Function. Transfer the dough to a lightly oiled mixing bowl and cover the bowl with clingfilm. Place in the fridge for 4 hours or, preferably, overnight.
4. Meanwhile, put the remaining butter (250g) between two sheets of baking paper. Using a rolling pin, roll it into a 15cm square, keeping the edges straight. Leave wrapped in the baking paper and chill for 30 minutes.
5. On a lightly floured surface, roll out the dough to a 30cm square. Place the butter on top at a 45 degree angle so that one corner of the butter is facing you. Fold over each corner of the dough to the centre to make a parcel. Use a pastry brush to brush off any flour. Press down the edges and flip upside down. Wrap in clingfilm and freeze for 10 minutes.
6. Once chilled, unwrap and roll out the dough to a rectangle of 20x50cm. Press firmly, but do not bash the dough.
7. Fold the top 1/3 down and the bottom 1/3 up so that the dough is folded up like a letter, making sure you keep brushing off the excess flour. Wrap in clingfilm and freeze for 10 minutes. This is called a turn.
8. Remove from the freezer, unwrap and place the dough in front of you so that the folded edge faces your right. Repeat the same rolling out, folding, freezing process another three times.
9. Take the dark chocolate (200g) and cut into strips about 1cm thick. If it cracks, do not worry, just keep the cracked shape together.
10. Remove the dough from the fridge and place on a floured surface with the folded edge on the left. Cut in half widthways, cover one half with clingfilm and chill again.
11. Roll the dough into a rectangle about 0.7cm thickness.
12. Cut into 5 rectangles widthways about 8cm wide.
13. Place a strip of chocolate on each pastry along one of the short sides, about 1cm away from the edge.
14. Fold over the edge to cover the chocolate and place a second strip of chocolate on the seam that was created by folding. Roll up the croissant with a gentle pressure and place on a large rectangular tray lined with baking paper.
15. Repeat Steps 11-14 with the other half of the dough.
16. Loosely cover the baking trays with clingfilm and leave them to rise at room temperature for another 1-2 hours, or until doubled in size.
17. Crack the egg (1) in a small bowl and add milk (1 Tbsp). Brush each bun with the egg wash and chill for 30 minutes.
18. Preheat the oven to 200C.
19. Transfer to the oven for 20 minutes, or until golden brown.

Freezer Tips:                                         

• Want to bake from frozen? Freeze the pastries after Step 16, brush with the egg and milk wash