Donut Dough

1. Combine flour, yeast, sugar, egg, milk and salt in the bowl of a stand mixer fitting with a dough hook
2. Combine the ingredients on low speed, before increasing the speed to medium-high and kneading for 5 minutes, or until smooth
3. Add the butter and continue to beat for 10 minutes
4. When the dough is slightly tacky, but doesn't completely stick to your fingers it's ready (more flour can be added if necessary, but don't add too much)
5. Transfer the dough to your counter-top, dust lightly with flour and shape into a ball
6. Place the dough back into the bowl and cover with cling wrap
7. Place the covered bowl in a warm area for 1-2 hours, until the dough has doubled in size
8. Remove dough from bowl and release built up air by flattening the ball
9. Dust with flour
10. Roll out to 0.5" / 1.5cm thickness
11. Cut out 2.5" / 6cm round circles using a round cookie cutter
12. Place cut out rounds on a sheet of baking tray lined with baking paper and cover with cling wrap
13. Place in a warm place for 1 hour, or until doubled in size
14. Cut the baking paper with scissors so that each ball is on it's own square of baking paper
15. Heat a pot of vegetable oil up to 170C / 340F
16. Carefully pick the donut up by the corners of the baking paper and place into the hot pot of oil
17. Fry for 2 mins on each side, or until golden brown, then drain on a wire rack or paper towel
18. Repeat with the remaining donuts, without overcrowding the pan (fry a maximum of three donuts at a time)
19. Roll the donuts in a bowl of caster sugar until well coated
20. Cool completely before filling

Filling

1. Once donuts have cooled combine cream and Nutella in the bowl of a stand mixer
2. Beat them together on medium speed until medium-stiff peaks, keeping an eye on the cream as you beat to prevent over-whipping
3. Transfer cream to a piping bag fitted with a small round piping tip 
4. Using a chopstick, or a thin and long utensil poke a hole on the side of each donut, taking care not to pierce the whole way
5. Give the utensil a little wiggle to create a pocket for the cream to fill
6. Place the tip of the piping bag into the donut and fill, leaving a small dollop of cream on top
7. Add another dollop of Nutella and sprinkle with roasted hazelnuts if desired
8. Enjoy!