Add the flour, yeast, salt and caster sugar to the bowl of a food processor. Attach the dough hook and mix at a low speed to combine the dry ingredients. Cut the cold butter into dice and add them to the mixture, mixing until fine breadcrumbs are formed.
Whisk together the milk and the egg and then add to the mixture. Increased the speed of the food processor until it is on maximum and work for a few minutes. Cover the dough with a damp cloth and rest for 10 minutes.
Turn the dough out onto a floured surface and knead for a minute or 2 before forming a ball and placing it back in the bowl. Cover again and rest for 1 hour until doubled in size.
Take the dough out of the bowl and very gently roll the dough to a thickness of 1cm. You can do this gently with your hands or use a rolling pin. Cover with a damp cloth and allow to rise again for half an hour. Use a cutter to cut rounds out of the dough and then use a small ring to stamp out a hole in the middle and form rings.
Deep fry the doughnuts at 190'C for 1 minute on each side. Remove with a slotted spoon and place on some kitchen paper to remove any excess oil. Cook only a few doughnuts at a time to avoid overcrowding the pan.
Place a bowl of chocolate over a pan of simmering water and allow to melt. This is called a bain marie and stops the chocolate burning through being in direct contact with the heat.
Dip the doughnuts in the chocolate so only one side is covered and put on a cooling rack to allow any excess to drip off. Place the cooling rack in the fridge to allow the chocolate to set for 5 minutes before enjoying.
«Try using milk chocolate or white chocolate as well. The cooking time will depend on the size of the doughnuts - larger ones may need a couple of minutes on each side.»