To make the pastry, dice the butter and place in a food processor with the flour, sugar and a grating of lemon zest. Pulse till you have fine crumbs.
Add the eggs and pulse till a dough is formed (you can also rub the flour, butter, sugar and a grating of zest together until they resemble fine breadcrumbs, then add the eggs and bring together to form a dough).
Wrap in clingfilm and refrigerate for 1 hour.
Use butter to grease a 25cm loose-bottom tart tin. Roll out the pastry to ½cm thick and use it to line the tin.
Trim and reserve the remaining pastry, then chill the lined tin in the freezer for 30 minutes.
Preheat your oven to 170ºC/325ºF/gas 3. Line the chilled tart tin with greaseproof paper, fill with baking beans and bake blind for 20 minutes, or until lightly golden.
Combine the cooked wheat, milk, vanilla and half the lemon zest in a saucepan and bring to the boil.
Reduce the heat and simmer until the wheat has absorbed all of the liquid. Remove from heat and allow to cool.
In a bowl, mash the ricotta with a fork, stir in the egg yolks, then beat until light and fluffy.
Sift in the icing sugar, then finely chop and add the candied peel, along with the orange-blossom water, orange zest and remaining lemon zest.
Beat until combined, then stir in the wheat mixture.
In another bowl, whisk the egg whites until stiff, then carefully fold them into the wheat and ricotta mixture.
Pour the filling into the tart case. Roll out the remaining pastry and cut into 2cm strips and use to create a rough criss-cross over the tart.
Bake the tart for 50 minutes, or until golden.
Allow it to cool, then dust with icing sugar. Serve slices with dollops of cream, scattered with orange zest and drizzled with honey, if you like.
Cooked wheat, also called wheat berries or grains, comes in a jar or can and is available from delicatessens.