Put the flour and butter into a food processor and pulse until the pastry just comes together and resembles rough breadcrumbs. Add the yolk of one of the eggs, reserving the egg white, and 2 tbsp ice cold water. Pulse again, then bring together into a ball with your hands. Wrap in clingfilm and set in the fridge to chill for at least an hour.
Preheat the oven to 200°C/fan 180°C/gas mark 6. Roll the dough out to 1cm thick and carefully line a 22cm tart tin with the chilled pastry. Prick the base all over with a fork, then cover the bottom and sides with greaseproof baking paper, making sure there is overhang covering the edges. Fill with baking beans and bake for 15-20 minutes, then remove the beans and baking paper and brush the bottom and sides of the pastry with the reserved egg white. Place back in the oven for 5-8 minutes, until lightly golden all over, then set aside to cool. Lower the oven to 160°C/fan 140°C/gas mark 3.
Meanwhile, whisk together the remaining eggs with the ricotta, cream and nutmeg, then season. Wilt the spinach in the microwave, then drain well and squeeze out any excess water. Stir the spinach, dill, lemon zest and spring onions through the eggs.
To assemble, carefully pour the filling into the pastry case. Use the pastry off-cuts to make a flower shape. Bake for 40-45 minutes until just set. Allow to cool slightly, before slicing to serve.