Place the flour, polenta, butter and a pinch
of salt into a food processor, then whizz until
the mixture resembles fine breadcrumbs. Tip
in the Parmesan and egg, then pulse through
2 tbsp cold water until the mixture forms a
ball. Wrap in cling film, then chill for 30 mins.
Dust a work surface with more polenta,
then roll out the pastry to the thickness of a £1 coin and wide enough to fit a 28cm tart
case. Gently ease into the case, then trim away
any big bits of overhanging pastry (leave a
little excess sticking up around the edges as
the pastry will shrink when cooking). Chill for
another 30 mins.
Heat oven to 200C/fan 180C/gas 6. Place
a sheet of baking parchment into the pastry
case, then fill with baking beans. Bake for
15 mins. Remove the beans and parchment,
then bake for another 5 mins or until the
pastry is golden. Leave to cool a little. Use
a serrated knife to trim away any bits of
overhanging pastry, then place the pastry
case on a baking sheet.
Reduce oven to 180C/fan 160C/gas 4.
Whisk the eggs and cream with a little salt.
Arrange the ham, tomatoes and watercress
in the case, then pour around the egg mixture.
Cook for 30 mins, just until the egg has set.
Can be made up to 1 day ahead and chilled.