This dip is so popular with my friends and students that I’ve been asked to manufacture it in bulk, bottle it and sell it to the public! As delicious as this is, however, it only takes a few minutes to prepare. I don’t suggest using a blender in place of a food processor since the blender tends to give the dip an undesirable mousse-like texture. If a food processor is not available, use a chef’s knife to mince together finely the tuna, scallions, anchovies and garlic before incorporating the remaining ingredients.
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Put all the ingredients, except capers, black peppers and accompaniments, into the bowl of a food processor fitted with the steel blade. Process until well blended. Remove to a bowl and fold in chopped capers. Grind in some fresh black pepper. (Or finely mince together all of the solid ingredients with a chef's knife and stir in mustard, mayonnaise, lemon juice and pepper.) Refrigerate (well covered) until serving time.
Surround the spread with assorted raw vegetables or a pile of hot slices of freshly broiled garlic toasts or a basket of warmed crackers or spread on slices of crusty Italian bread.
Make this spread two days ahead and refrigerate securely covered.
If serving this spread with assorted raw vegetables (crudites), the vegetables can be prepared a day ahead and kept well covered in the refrigerator.