Pulse flour, salt, butter, parmesan, egg yolks, and 10ml water in a food processor to form dough.
Wrap dough in cling film and chill in the fridge for one hour.
Salt diced courgettes in a sieve for 30 minutes to drain moisture.
Sauté sliced onions in butter until softened.
Rinse courgettes, squeeze dry, and cook with onions and chilli for 4 minutes.
Roll out pastry on a floured surface to 3mm thickness.
Line a 20cm tart ring with pastry and chill for one hour.
Preheat oven to 170°C.
Blind bake pastry with parchment and beans for 20 minutes until light golden.
Trim excess pastry, remove crumbs, and brush base with egg wash.
Reduce oven temperature to 160°C.
Combine cheddar with onion mixture and spread into the pastry case.
Boil cream, whisk in yolks until 82°C, then add whole egg and nutmeg.
Fill tart with custard and bake for 25 minutes until set.
Top with parmesan and brown with a blow torch.
Steam courgette flowers for 3 minutes and drizzle with oil and seasoning.
Cool slightly, slice, and serve with the steamed flowers.