flatleaf parsley, for sprinkling (optional)
1 spring onion, thinly sliced, for garnishing (optional)
1 tsp Dijon mustard
陆 tsp Worcestershire sauce
陆 tsp olive oil
录 tsp paprika
1 tbsp unsalted butter
1 large free-range egg
3 tbsp full-fat milk
3 tbsp finely grated Parmesan
2 slices white sourdough bread (see recipe tip)