1) In a large wooden salad bowl, mash the anchovies with a fork until they form a paste. Whisk in mustard and vinegar. Drizzle in the olive oil while whisking to create an emulsion. Adjust the seasonings and add salt and black pepper, to taste.
2) Add the escarole, green onions and olives to the bowl and gently toss to coat the leaves with the dressing.