Pour the warm milk into a jar and stir in the yeast. Leave for a few minutes until frothy.
In a large bowl whisk together the flour, salt and caster sugar. Create a well in the centre and pour in the frothy mixture followed by the melted butter and egg. Stir until well combined.
Tip dough out onto a floured work surface and knead for 5 minutes. Flour hands and surface as needed, however, the dough is meant to be sticky so try not to add too much extra flour.
Place dough back into the bowl and cover with cling film. Leave in a warm place until doubled in size (around 45 minutes to 1 hour).
Once risen, punch down the dough and knead for a few minutes. Divide evenly into 12-16 balls and place onto a baking tray leaving gaps in-between. Leave to double in size a second time (around 20-30 minutes).
Once risen fry doughnuts in vegetable oil at 190°C, 2 or 3 at a time, for 2-3 minutes. Make sure to rotate a few times. Place the cooked doughnuts on a sheet of kitchen roll to drain off excess oil. Once cool enough to handle, roll doughnut in caster sugar.
For the Nutella cream, heat double cream in a pan until very hot but not boiling. Pour over Nutella in a separate bowl and stir until smooth. Leave to cool and then place in the fridge. Whip up to thicken before serving.
For the funfetti fluff, add the egg whites, caster sugar, golden syrup, salt and vanilla extract into a heatproof bowl over a pan of simmering water. Beat for 4-8 minutes until doubled in size and stiff peaks form. It is ready when you can no longer feel sugar granules when you rub some of the mixture between two fingers.
Leave to cool before stirring in sprinkles (optional).
Optional - fill syringes with funfetti fluff, Nutella cream or jam and serve with the doughnuts! Enjoy :D