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.
Zest and juice both of the lemons.
Place the sugar, lemon juice, lemon zest, and butter into a saucepan and place onto a low heat. Constantly stir the mixture until the butter has melted. Leave on a low heat for 2-3 minutes until the the sugar starts to melt. Keep stirring the mixture. Remove the pan from the heat and quickly add in the whole egg and egg yolk. Whisk the mixture quickly and return the pan back onto the heat. After one minute remove the mixture. Place the curd into a bowl, cover with cling film and allow to cool.
When the mixture is cool, spoon into a piping bag and cut off the end to make a small hole.
Scrape the seeds from the vanilla. Mix the caster sugar with the seeds and then roll the doughnuts through the sugar.
To fill the doughnuts, make a small hole in the doughnut with a paring knife and insert the nozzle of the piping bag. Squeeze in enough filling and then roll the doughnut in the vanilla caster sugar.
«Experiment with the fillings for doughnuts. Try a chocolate ganache or a fruit compote.»