In the container of a blender, process half of parsley, egg, lemon zest and juice, hot sauce, mustard, garlic, and salt until smooth. With blender running, add oil in a slow, steady stream until fully combined. Add green onion, capers, and remaining parsley, and process until just combined. Transfer to a serving bowl, and garnish with green onion, if desired.
Notes
* Consuming raw or undercooked meats, poultry, seafood, shellfish, or eggs may increase your risk of foodborne illness. A pasteurized egg may be substituted.
Recipe by Louisiana Cookin' at https://louisianacookin.com/fried-snapper-and-shrimp/