Prick the duck all over with a fork to help release the fat. Put the herbs into its cavity.
Heat 2 tbspof olive oil in a heavy based casserole and brown the duck all over. If you do this slowly, it will release all the fat, so it can run out. Ladle some of the fat out of the pot and keep aside (wonderful for roasting potatoes.)
When nice and brown, pop it breast side down in the pot, cover with stock and simmer for 1 1/2 hours.
When done, turn the duck over and add the lettuce which has been shredded and the peas, season and replace the lid and cook for a further 40 minutes.
Take out the duck and carve or joint. Keep warm. Drain the peas and lettuce and put with the duck.
If necessary, skim off any fat off the sauce, season. Mix the yolks and cream in a basin and pour over half the stock. Mix well and then pour back into the rest of the sauce. Cook gently, but DO NOT boil.
Finally add the lemon juice and the mint and then pour over the duck and serve.
