Form ground round into 6 patties, or trim any fat from round, sirloin, or flank steak, and cut into 6 equal pieces. Place steak pieces, 1 at a time, between 2 sheets of heavy-duty plastic wrap, and flatten to 1/4-inch thickness using a meat mallet.
Combine breadcrumbs, salt, and pepper in a large shallow dish. Dredge patties or steak pieces in breadcrumb mixture. Dip into buttermilk, and dip again in breadcrumb mixture.
Heat oil in a large skillet over medium-high heat until hot. If desired, add corn tortillas, 1 at a time, and cook until crisp. Drain, pressing between layers of paper towels.
Add patties or steak to hot oil; cook 3 to 5 minutes on each side or until crisp. Remove from heat, reserving 3 tablespoons drippings if making Cream Gravy. Drain patties or steak on paper towels.
Place patties or steak on tortillas, if desired. Top with sauce of your choice, and sprinkle with cheese, if desired. Broil 5 inches from heat (with electric oven door partially open) until cheese melts. Garnish, if desired.
*1 cup all-purpose flour or 1/4 (15-ounce) box saltine crackers (about 40 crackers), coarsely crushed, may be sustituted for breadcrumbs.
** 1/2 cup milk a nd 2 large eggs, stirred together, may be sustituted for buttermilk.
Rancho Martinez Restaurant, Dallas, TX