Make the pastry by putting the flours and the salt in a food processor and pulse to mix. Add the egg, butter and oil and pulse until like small breadcrumbs.
Add the water a tablespoon at a time until the mixture is coming together in larger lumps. Remove from food processor, press together and cover and refrigerate for around 30 minutes.
Roll out to fill a pie dish or tart tin (approx 9in/23cm diameter but if shallow, I'd suggest wider), trim around the top and chill for another 30 minutes.
Preheat oven to 350F/175C.
Blind bake the pastry for 20 minutes (by covering the pastry with parchment paper/foil and filling with baking beans or dried beans). Then remove the filling and bake another 5 minutes uncovered until the pastry is dry. Set aside until fillings are ready or assemble immediately.
Meanwhile cook the bacon in a skillet/frying pan without any oil. Once the bacon has rendered a little fat (a couple mins), add the onion and cook until both are browning, around 15 minutes.
Dice the ham into small pieces and whisk together the eggs, cream, milk, pepper and nutmeg.
Assemble the filling by putting in a layer of ham, then bacon and onions, then grated cheese, and finally pour over egg-cream mix.
Bake for approximately 25 minutes until lightly browned on top and set.