Preheat oven to 160°C.
For the crust, mix all the ingredients in a food processor to form a soft dough.
Press the dough evenly into a 24 cm quiche dish.
For the filling, arrange the butternut on the base.
Heat the butter in a heavy-based saucepan and add the onion.
Sauté until translucent.
Spoon onion over butternut layer.
Sprinkle the feta cubes over the butternut and onion mixture, followed by the basil.
Beat the eggs, milk, sour cream and lemon juice together.
Add the Parmesan, mustard, salt and pepper.
Pour mixture over the tart.
Bake for 45 minutes or until golden brown and set.