Stir often over medium-high heat until onion is lightly browned, about 12 minutes.
03Add flour and mix well.
04Stir in beef broth and milk.
05Stir over high heat until boiling.
06Continue to boil, stirring constantly, until liquid is almost evaporated, 4 to 5 minutes.
07Remove from heat and stir in 1/2 cup shredded Swiss cheese and shredded Parmesan Cheese.
08Add salt and pepper to taste. (Makes about 1 cup).
09Rinse steak and pat dry.
10Pat salt, pepper and garlic flakes evenly onto meat.
11Preheat oven to 400°F.
12Pour oil in 10-inch non-stick pan and heat over high heat (tilt to cover bottom of pan with oil).
13When oil is hot, add steak and brown on both sides, about 4 minutes total.
14Supporting meat with tongs, tip steak onto its edge and rotate to brown lightly, about 2 minutes total.
15As fat accumulates in pan, wipe it out with paper towels.
16Put steak on oven-safe plate and bake in 400°F oven until meat is done to your liking, 8 to 12 minutes for rare or about 20 minutes for well done.
17Remove plate from oven.
18Turn oven heat to broil.
19Remove fat from plate with a paper towel.
20Mound French onions on meat and sprinkle with 1/2 cup shredded Swiss cheese.
21Broil in pan about 6 inches from heat until cheese bubbles and begins to brown, 3 to 4 minutes.
22Remove pan from oven and pour broth around meat, stirring to release browned bits.
23To serve, cut meat and onions into 4 equal portions.
24Transfer to individual plates and spoon juices around meat.