Optional flavor enhancer: Use a few teaspoons of oil from the sundried tomatoes to gently sauté the diced onion until golden. Then set aside and allow to cool.
pie dough
Add the flour butter and salt to the bowl of a food processor. Pulse until a sandy mixture forms (30-40 seconds). Add the egg and pulse just until the mixture clumps together and stop immediately (about 30 seconds more).
Sprinkle your work surface with flour and use your pie pan as a guide - trace its outline into the flour about 5 cm / 2 inches wider than the pie pan.
Prepare your pie pan or quiche pan by rubbing with butter then sprinkling with flour.
Roll out the dough to the traced outline, then place it in the prepared pan.
quiche filling
Crack the eggs into a bowl and whisk them up until even.
Add the diced onion and the rest of the quiche ingredients to the bowl (you can reserve some of the feta and tomato to garnish the top if you like).
Mix everything well and then pour into the pie, top with any reserved feta / sundried tomato.
Apply eggwash along any exposed pie dough, and then bake in preheated oven for 55 minutes or until evenly golden and cooked through (insert a toothpick in the center to check doneness).
Notes
If the top if browning too much, gently tent the top with aluminum foil being careful not to press it into the center of the quiche where the egg may not be cooked and could stick to the foil.