Boiled Beef Salad

Cut leftover sliced beef into wide slivers, and cut any leftover potatoes and vegetables into bite-size pieces. Make a fairly tart vinaigrette with Dijon mustard, red wine vinegar, salt and pepper, and olive oil. In a large bowl, combine the meat, potatoes, and vegetables with enough of the vinaigrette to moisten, adding a few capers and some chopped fres