Served with a big helping of mashed potatoes, gravy, and some steamed green beans, this is one of the great American diner traditions. Do not try to dress up the sandwich with good European-style bread; this is one case where spongy American white bread is right at home.
Very thinly slice:
About 1 pound cold roast beef
Prepare and keep very hot:
1 cup Basic Brown Sauce
Beat together until blended:
2 tablespoons butter, softened
1/4 teaspoon yellow mustard or 1 teaspoon drained horseradish
Spread this mixture over:
4 thick (1/2-inch) slices white bread or other soft bread of your choice
Layer the roast beef on top of the bread, douse generously with the hot brown sauce, and serve immediately.
