Add butter, milk, water, sugar and vanilla to a pot and bring to a boil on the stove.
Once everything is melted together, reduce heat to low and add in the flour.
Mix the flour in thoroughly and a dough ball will form.
Remove the pot from the stove and add the eggs one at a time until well blended.
Add dough to a piping bag fitted with a 1M or large star tip and place in the fridge for 10-15 mins to stiffen up a bit.
Combine sugar and cinnamon and set aside.
Heat the oil to 350.
Squeeze dough into hot oil.
Fry on each side for 3-4 mins until golden brown and cooked all the way through.
Remove from the oil and drain.
Toss in cinnamon sugar mix fully coating the churros.
Heat Nutella in a piping bag for 10-15 seconds.
Use a skewer to create a hole in both ends of the churro
Squeeze in the warm Nutella into the churros
Notes
The dough can be made ahead and placed in the fridge for up to 3 hours
Churros are best when fresh so batch fry if possible
For perfectly sized churros, pre-pipe the dough onto parchment or wax paper (after the dough has stiffened in the fridge-or it wont come off the paper).
Test one churro in the grease to make sure that your frying times are accurate. If the oil is too hot, it will brown the outside, leaving a raw middle, so check this before committing to frying off the entire batch.