Lightly grease an 8-inch, loose-bottomed tart tin.
In a bowl, whisk the flours with the salt.
Pour in the olive oil and water, whisk to combine with a fork and then lightly knead to bring the dough together.
Lightly flour the work counter and roll out the dough into a circle slightly larger ( 2-3 inches) than your tart tin. Turn the dough 45-degrees every time you roll so that you get a crust with even thickness. Sprinkle a little flour as you need, underneath, to prevent it from sticking to the surface.
Use your rolling pin to gently lift the dough and place it in the pan. Gently tuck the edges to fit the pan and trim any overhanging pastry around the edge of the tin.
Prick the base all over with a fork and chill the tart shell in the fridge for 30 minutes and in the meantime preheat the oven to 180°C.
After 30 minutes, bake the the quiche crust for 15 minutes. Remove and cool while you make the filling.
Make the filling
Heat 1 tbsp olive oil in a pan and saute the onions and garlic until soft.
Add the chopped tomatoes, salt, chilli flakes and dried herbs and cook till the tomatoes get pulpy.
Add the spinach and the sweet corn and cook till the water dries up. Cool the filling before spooning into the crust.
Assemble and bake the quiche
Preheat the oven to 180°C. Whisk the eggs with the milk, cream, pepper and salt in a bowl.
Place the quiche crust (still in the tin) on a baking sheet and crumble the feta evenly over the base (if using).
Fill the quiche shell with the spinach and corn mixture and then pour the custard over. Ensure no custard splashes over.
Bake the quiche for 20-25 minutes till the custard has set and the top is puffed. Cool the quiche on a wire rack for 15 minutes before slicing.
Notes
Total time includes the time taken to bake the tart shell, cook the filling and bake the quiche.