Preheat oven to 200°C. Sift flour and salt into a bowl and add butter.
Rub the butter lightly into the flour until the mixture resembles breadcrumbs.
Mix the water and egg yolk together and stir into the flour using a knife.
Wrap the pastry in cling film and place in the fridge for 30 minutes to chill before using.
Roll out the pastry and place it in a 28 cm loose bottom flan tin.
Chill for 15 minutes, before baking blind for 15 minutes.
Remove the baking aids i.e. paper and weights and return to the oven for another 5 minutes or until the pastry is golden brown.
Preheat oven to 180°C.
Heat the oil in a frying pan, add the onion and garlic and cookfor 2 minutes.
Add the bacon and mushrooms and cook for another 5 minutes.
Set aside to cool for 10 minutes.
Place in the base of the pre-baked pastry case and top with the cheese.
Lightly wisk the eggs, yolks, cream, milk and pepper in a mixing bowl.
Pour the egg mixture over the filling and bake in a preheated oven for 20 - 25 minutes or until the filling has just set.
Serve sliced, with oven-roasted vine tomatoes if desired.