Pulse flour and butter in a food processor until breadcrumb texture forms.
Add one egg and 15ml cold water and mix until combined.
Roll pastry to 3mm thickness and line the tart tin.
Prick the pastry base and chill in the fridge for 15 minutes.
Preheat the oven to 180°C.
Blind bake for 10 minutes with beans, then 15 minutes without.
Increase the oven temperature to 200°C.
Roast onions and courgettes with oil for 40 minutes until golden.
Reduce oven temperature back to 180°C.
Steam spinach, squeeze out all moisture, and roughly chop.
Whisk cream, eggs, and half the cheese together.
Layer remaining cheese, vegetables, and cream mixture in the pastry case.
Bake for 35 minutes until the filling is set and golden.