Wash the fish, if necessary cut off the skin and dice. Put into boiling salted water. Leave to stand for 8 minutes, remove and drain. Peel and finely dice the shallots.
Heat the lobster butter in a pot. Sauté shallots in it, dust with flour and sauté. Deglaze with stock and 1 cup of cream and boil thoroughly while stirring. Season to taste with salt, pepper and lemon juice.
Whip the remaining cream until stiff and fold into the sauce. Wash and halve the cherry tomatoes. Add fish, peas and tomatoes to the sauce. Garnish with tarragon.