Step 1

Prepare a large saucepan big enough for all the bones to be covered by the liquid.

Step 2

Place the fish bones into the saucepan. Cut the lemon in half, roughly chop the celery and cut the onion into quarters (keeping the skin). Put it all into the saucepan along with the bay leaf, parsley, salt and peppercorns.

Step 3

Pour in the water and champagne, bring to a simmer and cook for 30 minutes.

Step 4

Remove from the heat and strain through a sieve covered in a piece of muslin cloth into a large bowl or jug. Wait for it to settle and skim off any residue from the top.

Step 5

Finely dice the shallot.

Step 6

Heat butter in a saucepan and when it stops crackling, add the shallot and gently fry until softened.

Step 7

Pour in the champagne and bring to a gentle boil. Reduce the volume by a third.

Step 8

Pour in the fish stock and cream, bring back to the boil and reduce down by half.

Step 9

Season the champagne cream sauce at this stage with salt and pepper.

Step 10

Sieve the sauce to remove the shallot, return to the pan and heat gently to bring the temperature back up to just below the simmering point.

Step 11

Turn the heat off and whisk in a few extra cubes of cold butter to get a smooth and glossy finish. Serve immediately.