Prick the duck skin with a fork and place the herbs into the cavity.
Heat olive oil in a casserole and brown the duck slowly to release the fat.
Remove excess fat, place duck breast-side down, cover with 275ml stock, and simmer for 90 minutes.
Turn the duck over, add the shredded lettuce and 500g peas, then simmer covered for 40 minutes.
Remove the duck to carve, then drain the peas and lettuce and set aside together.
Whisk egg yolks and 55ml cream with some stock, then stir back into the sauce without boiling.
Stir in the lemon juice and mint before pouring the sauce over the duck to serve.