Preheat an oiled skillet to high heat until extremely hot. Add 1 tsp kosher salt to the pan.
Place steak into the skillet. Cook without moving until the bottom is seared (about 1-2 minutes), flip, do the same again. Continue flipping the steak until the thermometer reads 125° for rare.
Remove, let rest before slicing. Slice onion into half rings. Using the same skillet, saute onions and mushrooms until they get golden brown. Remove the onions from the heat and set aside.
Slice baguette lengthwise, add slices of steak, onion and topping it off with cheese slices. To melt the cheese place under the broiler for 10-30 seconds at a time.
Lastly, drizzle with Terrapin Ridge Farm's smoky and creamy Bacon Aioli. Serve hot!