• 2 lbs (900 g) whole prawns (yields 6 ozs (170 g) prawn tails approx.)
• 1 oz (30 g/¼ stick) butter
• 4 pints (2.3 L/10 cups) water
• 2 tablesp. salt

Bretonne Sauce

• 1 egg yolk (preferably free-range)
• ½ teasp. French mustard (we use Maille mustard with green herbs)
• 1 tablesp. mixed finely chopped chives, fennel, parsley and thyme
• 3 ozs (85 g/¾ stick) butter

Garnish

• flat parsley or fresh fennel

Bring to the boil 4 pints (2.3 L/10 cups) of water and add 2 tablespoons of salt. De-vein the prawns. Toss them into the boiling water and as soon as the water returns to the boil, test a prawn and then remove immediately. Very large prawns may take ½–1 minute more. Allow to cool and then remove the shells.

Next make the Bretonne Sauce. Whisk the egg yolks with the mustard and herbs in a bowl. Bring the butter to the boil and pour it in a steady stream onto the egg yolks, whisking continuously until the sauce thickens to a light coating consistency as with a Hollandaise. Keep warm in a flask or place in a pottery or plastic bowl (not stainless steel) in a saucepan of hot but not boiling water.

Just before serving, toss the prawns in 1 oz (30 g/¼ stick) foaming butter until heated through. Heap them onto a hot serving dish. Coat with Bretonne Sauce. Garnish with flat parsley or fresh fennel and serve immediately.