In blender, or by hand, mix water and The Good Oil into flour until just combined. Wrap in cling film and chill for 1-2 hours.
Heat 2 tbsp of The Good Oil in pan, add onions and a pinch of salt. Cook gently until well softened and golden. Add balsamic and cook for 5 minutes. Cool.
Coat asparagus in 2 tbsp of the The Good Oil. Cook gently in a pan for about 5 minutes. Until just cooked but still with some crunch. Season with salt and pepper.
Roll out the pastry and line a 24cm loose bottom dish.
Cover the base with onion and arrange asparagus evenly over the top. Cover with the salmon pieces.
Beat eggs and cream, add herbs. Pour over the onions, asparagus and salmon.
Cook at 180C for about 25 minutes, or until the top is brown and egg mix set.