Heat oven to 200C/180C fan/gas 6.
Roll the pastry out on a floured surface
to fit a 23cm fluted tart tin. Line the case
with pastry, leaving plenty of overhang.
Line the pastry with baking parchment,
fill with baking beans and sit it on a
baking sheet. Bake for 15 mins, until the
pastry looks pale and feels a little sandy.
Remove the paper and beans, then
return to the oven for 10 mins more,
until just golden.
Meanwhile, bring a pan of water to a
simmer. Drop in the haddock, skin-side
down, and poach for 5 mins or until the
flesh turns white. Drain, then cool a little.
Peel away and discard the skin, then
flake the flesh into the pastry case.
Look out for any bones as you go.
Melt the butter in a frying pan, then
gently cook the spring onions for about
3 mins or until softened but still a vibrant
green. Beat the eggs, crème fraîche or
cream, mustard and saffron together in
a jug, then add the chives and season
with salt and pepper.
Turn oven down to 160C/140C fan/gas 3.
Scatter the cheese and spring onions
over the fish, then pour the egg mix over.
Bake for about 50 mins, or until pale
golden and just set in the middle. Let the
tart cool completely before trimming
the pastry around the edges. Leave the
tart in its tin to transport. The tart is also very good hot or warm.