Heat oven to 200C/180C fan/gas 6.
Put the flour and cinnamon in a food
processor, then add the butter. Process
to make fine crumbs. Reserve 2 tbsp of
the sugar, then add the remainder and
briefly mix. Add the egg yolk and 1 tbsp
water, then pulse to make a firm dough.
Turn out onto a lightly floured surface and
briefly knead. Wrap in cling film and chill
for 30 mins.
Toss apricots in the reserved sugar. Roll
out pastry on a sheet of baking parchment
to a roughly 30cm round. Slide the paper
and pastry onto a large baking sheet.
Sprinkle the central 20cm with the polenta,
then cover with apricot halves, cut sides
up. Flop edges of the pastry over the
apricots, leaving the centre uncovered.
Lightly beat egg white and brush over the
pastry. Sprinkle with remaining sugar, then
bake for 30-35 mins until the pastry is
crisp and the apricots tender.