Scrub the mussels thoroughly under cold running water. Use scissors to cut off the beard where necessary. Discard any mussels that are already open as these are inedible. Heat the oil in a wide pan. Add the garlic, sauté for approx. 1 min., add the mussels, cover and cook for approx. 1 min. Pour in the wine, cover and simmer for approx. 4 mins. until the mussels open, stirring once. Discard any mussels that have not opened as these are inedible. Take the mussels out of their shells, place half of the shells on a baking tray lined with baking paper.
Heat the butter in a pan. Add the flour and cook over a medium heat, stirring with a whisk. The flour must not take on any colour. Pour in the milk and bring to the boil while stirring. Reduce the heat, season and simmer for approx. 2 mins. over a medium heat, stirring occasionally until the sauce is thick and creamy.
Mix the breadcrumbs, cheese, parsley and garlic. Add the butter and rub together using your hands to form an even, crumbly mixture. Place the mussels in the shells. Pour the sauce over the mussels, top with the crumb mixture and press down gently.
Approx. 4 mins. in the upper half of an oven preheated to 220°C.