Wash, scrub and debeard the mussels. Wash and scrub the cockles (small clams.) Put the prepared mussels in a large saucepan. Add 1/2 pint water, bring to a boil, cover and cook quickly for 5 minutes. Shake the pan occasionally during cooking. Add the cockles and continue cooking for a further 3-5 minutes. When the shells open, the shellfish are cooked. Any opened shells should be discarded. Remove the cockles and mussels from the shells.
Roll the bacon rashers (just plain bacon works)and neatly secure with a wooden cocktail stick (toothpick). Put in a pan of boiling water for a few minutes to remove the salt and set the rolls. Drain, dry and discard the cocktail sticks (toothpicks).
Melt butter in a large frying pan and fry the bacon until colored. Remove from the pan and keep warm. Fry the onion until soft, the add mussels and cockle, herbs, salt and pepper. Toss in the butter and heat thoroughly.
Divide between 4 warm serving plates, scatter over the bacon rolls and garnish with a sprig of watercress.
Serve with Irish Oakcakes and a pint of Guinness.
This can be made entirely with either mussels or cockles and served as a main dish with boiled potatoes. For a main course, double the quantities.