Preheat an oven 215°C. On a baking sheet toss the cauliflower with olive oil, salt, and pepper and roast for 30 minutes, flipping halfway. Allow to cool completely.

Reduce the oven temperature to 190°C. Roll out your dough and transfer to a 9" pie tin. Poke several holes in the dough on the bottom then blind bake the crust for 8-10 minutes until it just faintly changes color. Set aside to cool completely.

In a small frying pan, heat a small amount of olive oil and then turn the heat down the low and add the onions, cooking them slowly for 20-30 minutes until they caramelize.

Place the caramelized onions and cauliflower in the pre-baked crust, spreading them out evenly.

In a large bowl combined the eggs, mustard, cream, and seasoning and whisk very well until completely combined. Add the Gruyere then pour the entire mixture over the vegetables in the crust, coating them. Top with parmesan cheese and then bake at 190°C for 35-40 minutes.