Method

In a large mixing bowl weigh out the flour and the butter (chilled straight from fridge preferably from a block).
Make sure your hands are clean and then rub the butter into flour with fingers getting as much air into it as you can by using a light touch. Continue until mixture resembles fine breadcrumbs.
Add 2 teaspoons of chilled water to the flour/butter mix. Use hands to mix it in (I find that the best way is to make a claw shape with my hand and then use a twisting wrist motion to do the mixing). Continue adding water a little at a time until pastry just begins to bind together.
If you can make one big ball out of the pastry then you have added enough water, but if it won’t bind into a single ball add just a little water until it will. The ball should still feel fairly dry and will probably have lots of cracks on the surface but as long as it’s sticking together that’s okay.
Put the pastry in the fridge to chill.
Pre-heat the oven to 220 C / Gas 7. Chop the onion and slice mushrooms.
While oven is warming up, fry mushrooms and onion in the oil and garlic until just cooked through.
Grease your flan tin (if using) or get foil trays ready. Retrieve pastry from the fridge while veg is cooking.
Roll out the pastry to 3mm (1/8 in) thick, fold over rolling pin to lift it over the flan dish.
Press pastry into flan dish with back of your index finger. Prick bottom with a fork and trim off excess pastry and blind bake for 10 minutes.
Remove pastry cases from the oven when light golden brown and firm to touch.
Turn oven temperature down to 160 C / Gas 3.
Measure out milk into a jug and break 2 eggs into it. Beat hard with a hand whisk until light and bubbly. Add garlic powder, if using.
Share cooked veg between both flan cases (or spread out over bottom of case if using larger tin). Carefully pour egg/milk mix over the veg. Make sure that you don’t over fill the pastry case(s).
Grate enough of cheese of your choice to lightly cover the surface of quiche(s) and sprinkle over them. Sprinkle a little paprika over the quiche(s) for colour.
Bake in the oven for 30 minutes until the tops are golden brown and the mix feels firm. Enjoy!