In food processor, place 4 tablespoons olive oil, celery, green onions and parsley. Purée until smooth. Transfer mixture to bowl.
Stir in Dijon mustard, wasabi powder, lemon juice, mayonnaise, dry mustard, garlic, anchovy paste and 1/4 cup olive oil. Mix well.
Return mixture to food processor. Process on low speed 1 minute.
Pour sauce into sealable jar or bottle. Refrigerate until ready to use.