Cut the butter from Ingredients 2 into cubes and leave at room temperature to soften.
Leave the butter from Ingredients 3 at room temperature to soften.
Fit the K beater to the machine.
Grease the loaf tin.
Add Ingredients 1 (milk, plain flour, bread flour, salt, sugar, yeast, eggs) into the Mixer bowl.
Attach the Mixer bowl to the machine and fit the splash guard.
Mix on speed 2 for 5 minutes.
Add Ingredients 2 (butter) into the Mixer bowl.
Mix on speed 3 for 1 minute.
Scrape down the bowl.
Mix on speed 3 for 5 minutes.
Cover with a tea towel.
Leave to prove for 1 hour.
Chill in the fridge for 30 minutes.
Add Ingredients 3 (butter, sugar, dark chocolate, cinnamon) into the saucepan.
Heat over a medium heat until melted.
Leave to cool.
Transfer the chilled dough to a floured worksurface.
Roll out into a large rectangle.
Spread the melted chocolate mixture over the surface of the dough.
Roll up the dough tightly using the long edge.
Place the dough so the seam is underneath.
Cut the dough lengthways down the centre.
Twist the dough lengths around each other.
Place the dough into the loaf tin.
Leave to prove for 30 minutes.
Pre heat the oven to 180ºC.
Brush Ingredients 4 (egg) over the loaf.
Bake for 1 hour at 180ºC.
Cover with a foil if the loaf begins to burn.
Let cool for 10 minutes.
Turn out onto a wire rack.
Serve.