Place the flour, caster sugar, salt, yeast, eggs, lemon zest and cold water in a mixing bowl and mix together using the beater attachment of a hand or electric mixer for 8 mins at a medium speed.
When the dough becomes smooth and shiny, stop mixing and let it rest for 1 minute.
Then gradually mix in the melted butter and continue to mix for a further 5 minutes.
Remove from the bowl and bring together with a little flour. Cover with cling film and let it prove until it doubles in size - approximately 2 hours.
After it has risen, knock it back and place it in the fridge overnight.
Take the dough out of the fridge and shape into approximately 20 X 25g balls. Place on a tray and leave to prove for approximately 4 hours.
Get a heavy based saucepan and fill with 1.5 litre of the oil. Heat gently to approximately 175/180C. Place balls into the pan and cook for 2/3 mins on either side ensuring to turn.
When the doughnuts are cooked, remove and place in a bowl with caster sugar.
To make the chocolate sauce, put all the chocolate sauce ingredients in a bowl over a saucepan of water to melt gently. When the chocolate starts to melt, mix everything together and remove from the heat.
Place the little doughnut balls on a nice fancy plate and drizzle with chocolate sauce.
