Put the milk in a small pan with the shallots and peppercorns then bring to the boil.
Remove from the heat and leave to infuse for 15 minutes. Strain through a fine sieve.
In another saucepan, put the tomatoes in boiling water for 15 seconds, remove and peel away the skin.
Cut the tomatoes in half and discard the seeds then slice into thin strips.
Melt 15g of butter in a small sauce pan, stir in the flour and with the help of a wooden spoon and cook for approximately 1 minute.
Take off the heat and gradually stir in the infused milk. Season with salt.
Bring the white sauce to the boil, stirring constantly and gently simmer for 2 minutes. Whisk in the tomato paste and basil.
In the meantime melt the remaining butter in a frying pan and cook the fish skin side down for 2 minutes then turn and cook the other side for a further 2 minutes.
Meanwhile add the tomato strips to the sauce with the lemon juice stir and reheat gently.
To serve, place 2 pieces of fish on a serving plate and pour over the basil and tomato sauce.