A juicy, tender steak and cheese sandwich
Heat 3 Tbsp olive oil in a large skillet over medium heat. Add the sliced onions and cook until they are golden-brown and caramelized - about 20 minutes. Be careful not to burn as this will impart a bitter taste. Set the onions aside.
For the jus: Heat up a rich beef stock. Finish with 1/8 tsp balsamic glaze. Reserve and keep hot.
Season the medallions with kosher salt and turbinado sugar.
On a flat skillet, heat the remaining oil and sear the filet mignon medallions - about 1 to 2 minutes per side. Set aside.
Take 4-5 ounces of the caramelized onions and place onto a pan to heat up. Cover the onions with 2 slices of Monterey Jack cheese and allow the cheese to melt over the onions.
Toast the baguette so that the outside is hot and crusty.
Slice the baguette lengthwise, leaving halves attached on one side (like a hinge).
Ladle 2 ounces balsamic jus on the inside of the top half of the baguette.
Place the filet mignon medallions on the bottom of the baguette.
Finish by topping the medallions with the caramelized onions and cheese.