Put all the dough ingredients apart from the butter into the mixer bowl and beat on a medium speed for about 8 minutes, or until the dough starts coming away from the sides and forms a ball.

Let the dough rest for one minute.

Start the mixer up again on a medium speed and slowly add the butter – about 25g (0.9oz) at a time.

Once it is all incorporated, mix on high speed for 5 minutes, until the dough is glossy and elastic when pulled.

Cover the bowl with clingfilm and leave to prove until it has doubled in size.

Knock back the dough, then re-cover the bowl and put into the fridge to chill overnight.

The next day, take the dough out of the fridge and cut into around 20 pieces weighing 50g (1.8oz).

Roll them into smooth, tight buns and place them on a floured baking tray, leaving plenty of room between them.

Cover lightly with clingfilm and leave to prove again for about 4 hours, or until doubled in size.

Prepare your deep-fat fryer, or fill a heavy-based saucepan to the halfway point with sunflower oil and heat to 180C (356F).

Carefully remove the doughnuts from the tray and put them into the oil, frying for two minutes on each side until golden brown.

Remove from the fryer and place on kitchen paper, then toss them in a bowl of caster sugar while still warm.

To fill, make a hole in the crease of each doughnut and pipe in your desired filling.