Take out Unsalted Butter (4 tablespoon) 1-2 hours before making the sandwich. This will allow it to soften.
Preheat the oven to 425 degrees F (220 degrees C).
Take out the Boneless Ribeye Steak (16 ounce) from the refrigerator and immediately cut while still cold. Remove any large areas of fat and toss it out.
Place the steak horizontal to you and slice as thin as possible. The slices should be short and thin. Sprinkle with Salt (1/2 teaspoon).
Heat a cast-iron or sauté pan on high heat with Avocado Oil (1 tablespoon). When the pan is hot, place the thin-sliced steak spread out. Sear both sides for 2 minutes each, until browned on each side.
Do in sections until all steak is seared and let sit and rest on a cutting board or plate.
Spread the butter on one side of all slices of Sourdough Bread (8 slice), 8 sides in total.
Place 4 bread slices butter side down on an aluminum-lined baking tray.
Place one slice of White Cheese (4 slice) on top of each piece of bread.
Add thin-sliced steak onto each bread slice. I used around 5-6 slices of steak per bread slice but will depend on how much steak you have.
Place White Cheese (4 slice) evenly on top of steak (around ½ cup each) and top with remaining slices of Arugula (2 cup) per bread slice.
Put top bread slice on top, butter side facing up.
Put the baking tray with the uncooked sandwiches into the oven. Bake for 15 minutes.
Broil on High for 2 minutes, watching very carefully to ensure the top slice doesn’t burn.
Remove from oven immediately and cut in half or enjoy whole!