Warm milk and butter together in a saucepan, then take it off the heat when the butter is melting. Put flour, yeast, salt and sugar in a bowl. Beat egg into warmed milk and pour into bowl of dry ingredients.

Using a dough hook or your hands, knead the dough until it is smooth and silky - about 10 minutes by hand.

Place in a greased bowl, cover with clingfilm and allow to rise in a warm place until doubled in size, between one to two hours.

Punch the dough down and knead again to make smooth. Cut in half and roll into two 25cm logs. Cut each log into 12 pieces, roll each into a rough ball and place on a baking paper-lined tray. Cover loosely and allow to rise for a further 15 minutes.

Heat oil in the deep-fryer to 190C. Cook the doughnuts, a few at a time, for five minutes, flipping over halfway so they brown evenly. Remove and drain on a paper towel, then roll in sugar to coat.

Place jam in a piping bag with a small nozzle (or use a sauce bottle with a plastic nozzle) and pipe a small amount of jam into the centre of each doughnut.