Heat the milk and butter in a pan until just warm. Add the flour, yeast, sugar and salt to the bowl of a food mixer. Using the dough hook, mix to combine then slowly pour in the warm milk mixture and it should start to slap around the sides of the bowl. Scoop it out and sit it on a lightly floured board and knead it for about 10 mins until silky smooth and it bounces back when you indent it with your knuckle. Put the dough in a bowl, cover with cling film and put somewhere warm for a couple of hours until it doubles in size.
Meanwhile prepare the filling: add the chocolate to a heatproof bowl, sit it over a pan of barely simmering hot water and stir until the chocolate melts. Remove from heat and stir in the cherries. Put to one side. Now knock back the risen dough and turn it onto a lightly floured board. Divide it up equally into four pieces.
Roll out each piece into a rectangle about 15 cm x 40 cm, it will keep springing back, but persevere and give it a little stretch if needed. Now divide the chocolate and cherry mixture up between each rectangle, spooning it in, just off centre then roll it up lengthways so you have four long tubes, lay them on the board seam side down. Gather the four tubes at the top and secure them together. Then starting from the right hand side, do a regular plait with the first three tubes, then stretch the fourth under and continue like this, plating three then the forth one under each time. At the end, secure the end pieces together and neaten. Transfer the plait to a large baking sheet, cover with a clean tea-towel and leave somewhere warm for 30 mins for it to double in size again. Preheat the oven to 200C/180C/Gas 6. Remove tea-towel, brush with a little of the egg wash and put in the oven for about 30-40 mins or until it feels hollow when tapped underneath. Remove from oven and leave to cool a little on a wire rack. Dust with icing sugar and slice to serve.
MAKE IT VEGAN
Switch the butter milk for unsweetened almond milk or use your favourite plant based milk and switch the butter for a plant based butter. Omit the egg wash and brush with a little of the almond milk.