flatleaf parsley, for sprinkling (optional)
1 spring onion, thinly sliced, for garnishing (optional)
1 tsp Dijon mustard
Β½ tsp Worcestershire sauce
Β½ tsp olive oil
ΒΌ 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)