In a medium saucepan, cook onion and garlic in butter until tender. Add well-drained spinach to onion mixture; cook and stir until just heated through. Remove from heat. Stir in bread crumbs, Parmesan cheese, salt, and the 1/8 teaspoon pepper. Set the spinach mixture aside.

Using a long, thin knife, insert the blade into one end of the beef tenderloin. Cut to, but not through, the length of the loin to butterfly the meat. Spread the tenderloin open. Sprinkle the cut surface with a little salt and pepper. Spoon spinach mixture along length of tenderloin. Close tenderloin; tie securely in several places with kitchen string. Ruboutside of beef tenderloin with the 2 teaspoons coarsely ground pepper.

Place the stuffed beef tenderloin on a rack in a roasting pan. Insert a meat thermometer into the meat. Roast, uncovered, in a 425 degree F oven for 30 to 45 minutes or until thermometer registers 145 degree F (for medium-rare).

Remove roast from oven. Cover loosely with foil and let stand for 10 minutes. Slice to serve. Makes 8 to 10 servings.