Heat oven to 200C/180C fan/gas 6.
Roll out the pastry and use to line
a 23cm loose-bottomed tart tin. Prick
the base with a fork and line with baking
parchment and baking beans. Sit the tin
on a baking sheet and bake for 10 mins,
then remove beans and parchment and
return to the oven for a further 5 mins
until pale golden. Reduce oven to
180C/160C fan/gas 4.
Meanwhile, melt the butter in a large
pan and gently cook the leeks for 10 mins
until softened. Beat together the ricotta,
cream, eggs, tarragon, a little salt and
plenty of black pepper. Stir in the leeks
and all but a handful of the cheese.
Pour the mixture into the tart case and
scatter over the remaining cheese. Bake
for 25-30 mins until golden and set. Leave
to settle for 5 mins, then carefully
remove from the tin and allow to cool
a little on a wire rack. Serve warm.