Divide the pastry in two, roll each piece out as thin as possible, then stretch over the backs of your hands (the pastry should now be so thin you can see through it) to give 2 sheets about 60 X 45 cm/24 X 18 inches. Allow the pastry to dry out slightly, then cut each sheet into 12 squares of about 15 cm/6 inches. Take 6 tins, such as brioche tins, about 10 cm/4 inches across and 5 cm/2 inches deep. Lay 4 pastry squares in each tin, one on top of the other so that the points of the squares make a petal formation.
Peel the asparagus tips and plunge into boiling salted water for 2 minutes, then refresh in iced water and drain. Bring the vinegar and half of the fish stock to the boil. Remove the heads from the prawns (save them for another recipe) and plunge the tails into the boiling stock; cover and simmer for 3 minutes. Drain the tails from the stock and allow to cool.
To make the prawn sauce, return the stock to the boil and reduce by two-thirds. Meanwhile, for the second sauce, bring the white wine and remaining fish stock to the boil in a separate pan and reduce by two-thirds. Add about 85 g/3 oz of the shallots and 85 ml/3 fl oz of the cream, return to the boil and reduce slightly. When the prawn stock has reduced, add the remaining shallots and the carrots along with the rest of the cream, then return to the boil and reduce slightly.
Shell and cut each prawn in half. Cut each asparagus tip slightly at an angle into 3 or 4 pieces. Bring the prawn sauce to the boil, then remove from the heat and gradually add 85 g/3 oz of the butter, shaking the pan continuously until all of the butter has melted. Add the prawns and asparagus, then leave over a very low heat until the other sauce is ready (do not allow the sauce to boil once the butter has been added).
Bring the second sauce to the boil, remove from the heat and gradually add the rest of the butter, again shaking the pan until it has all melted. Pour a little of the sauce onto each plate. Add the chervil to the prawn sauce and divide out between the filo cases. Place one case in the middle of each plate. Serve immediately.
© 1989 Ian McAndrew. All rights reserved.