To prepare the mussels, put into a sinkful of cold water, throw away any that are broken or any that stay open when you tap them on a hard surface. Pull away the beards (the hairy bits between the shells). Scrub the shells and put into a colander, rinse with fresh cold water then drain well.
Heat the oil in a pan large enough to hold the mussels. Add the shallots and garlic and fry gently for 4 to 5 minutes until softened but not browned.
Add the beer and pinch sugar to the pan, turn up the heat and bring to the boil. Boil for 3 minutes.
Add the mussels, cover with a lid and cook, stirring frequently to make sure they are evenly cooked. This will only take a few minutes until the mussels have opened and are cooked. Remove any mussels that have not opened.
Spoon into warm serving bowls with the juices; sprinkle with parsley.