In a small bowl, cover the anchovy fillets with the milk and let soak for 30 minutes. Drain the anchovies and add them to a food processor along with the olives and mustard. Process to a paste. With the machine on, slowly pour in the olive oil to make a smooth puree. Top each Crostini Toast with a heaping teaspoon of tapenade.
The tapenade can be refrigerated for up to 1 week.