• Preheat oven to 400 °F/200 °C with the rack in the center of the oven. Grease a 9-inch (23 cm) round quiche/tart pan preferably with a removable bottom.

Make the Pastry in the Food Processor:

• Add the flour, butter and salt. Pulse until you get the texture of fine breadcrumbs. Add 1 tablespoon of cold water. Pulse a few times until you start to see the dough come together, adding a little water as needed. Remove the lid and grab a little dough, if it holds together (without being sticky) it is done. If It crumbles pulse more adding small amounts of water. Test again using the squeeze test.

Make the Pastry by Hand:

• Add the flour, butter and salt to a large bowl. Using your fingertips (or a pastry cutter) rub the butter and flour until it resembles breadcrumbs. Add a little of the water and mix using a fork until the it starts to come together and holds together when pressed in your hand. You may not need all of the water.
• Pour the dough onto a lightly floured surface and form into a flat disk. Wrap in plastic wrap and refrigerate 30 minutes. .

Cook the Filling:

• To a sauté/frying pan, cook the bacon over medium heat. Drain and set aside. Keep bacon fat in pan.
• Return the pan over medium heat and add the mushrooms and squash, and cook until they start to soften. Add the leek and cook until the squash is tender when pierced with a fork, do not brown. Stir in the sage, salt and pepper. Turn off the heat and set aside. 

Mix the Custard:

• To a mixing bowl add the eggs and milk, whisk until combined. Add the nutmeg, salt, pepper and whisk until combined.
• Add the bacon, leeks, mushrooms and butternut squash to the milk and eggs and mix well. Stir in the cheddar cheese. Set aside.

Blind Bake the Crust:

• Remove the pastry from the refrigerator and roll out onto a lightly floured surface, larger than the quiche pan.
• Roll the pastry over your rolling pin and lift it into the pan, pressing it firmly into the bottom and up the sides. Leave a slight overhang to account for natural shrinkage during baking. Press out any cracks with your fingers.
• Place the tart pan on a large baking sheet for easy handling. Lightly line the crust with a sheet of parchment paper and fill the center with dried beans, peas, or uncooked rice to weigh it down.
• Bake the crust for 10 minutes. Remove from the oven, carefully lift out the parchment paper and beans, and return the bare crust to the oven for 5 more minutes.
• Remove from the oven and let cool for a couple of minutes. Turn your oven temperature down to 350°F/180°C.

Assemble and Bake:

• Pour the filling mixture into the warm crust, using a fork to make sure the vegetables are evenly distributed. Top with an even layer of freshly grated Parmesan cheese.
• Bake for about 30 minutes, or until the custard is set and the top is slightly golden brown.
• Remove from the oven and allow to cool for 10 minutes on a wire rack before removing the outer ring of the pan, slicing, and serving.