In a machine use the dough hook attachment and add the flour, yeast, salt and caster sugar. Turn on to a low speed for a minute so all the dry ingredients are well mixed together. Dice the cold butter and add until fine breadcrumbs are formed. Whisk the egg and milk together and pour into the mix, gradually turn the speed of the blender to full speed and work for a few minutes. Turn off, cover with a damp cloth and rest for 10 minutes. Turn 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. Turn back out onto the work surface and cut into 30g balls. Roll and place onto an oiled tray. Oil a long sheet of cling film and cover for the final prove.
Deep fry at 180'C for 1 minute on each side. Remove with a slotted spoon and place on some kitchen paper to remove any excess oil
Mix the caster sugar with the ground cinnamon and then roll the doughnuts through the sugar.
Fill a piping bag with jam and cut off the point. Use the tip of the knife to make a small hole in the side of each doughnut and fill with jam.
«Vary this recipe by glazing the doughnuts with a chocolate sauce or vanilla frosting.»