Heat oven to 200C/fan 180C/gas 6.
In a small bowl, mix the grated cheddar
with the crème fraîche, then set aside.
Grease and lightly flour a ceramic or
metal pie dish, or shallow cake tin,
about 23cm wide. Roll out two-thirds
of the pastry on a lightly floured surface
until large enough to line the tin with
a little overhang.
Place a layer of potatoes over the tart
and scatter over some of the sliced
onions, spring onions and chunks of
cheese. Season with salt, pepper,
nutmeg and paprika. Layer over more
potatoes, scatter again with more
onions and cheese, then splodge over
half the crème fraîche mix. Repeat with
2 more layers (the potatoes will come
up way above the pastry), pushing the
filling down slightly, then finish with the
remaining crème fraîche mix.
Roll the remaining pastry so it fits
over the potatoes. Brush the sides with
egg, then lay the pastry over the top.
Squeeze the edges together and trim
with a knife. Crimp the sides and brush
the top all over with egg. Place the pie
on a baking sheet, bake for 30 mins,
reduce the temperature to 180C/
fan 160C/gas 4, then carry on baking
for 1 hr until golden. Leave the pie to
rest for 10 mins, then serve straight
from the dish cut into slices, with a
salad or baked beans on the side.