Step 1

Preheat your Blackstone over medium-high heat.

Step 2

Mix 1 teaspoon each of salt, black pepper, onion powder, and granulated garlic.

Step 3

Butter all the hamburger buns with 2-3 tablespoons of butter. Place butter-side down on the griddle and let brown. Remove and set aside once they are toasted.

Step 4

Put the remaining butter down on the griddle and place the sliced onions on the butter. Sauté for 5 minutes, flipping frequently.

Step 5

Put the steaks on the preheated griddle and cook for 3-4 minutes per side.

Step 6

While the steaks are cooking, whisk together the aioli ingredients.

Step 7

Once the steaks are cooked to your liking, remove them from the griddle and rest for 5 minutes.

Step 8

After resting, slice against the grain and build your sandwiches with the steak, cheese, sauteed onions, and horseradish aioli.

Step 9

If desired, you can melt the cheese on the sandwiches by briefly putting the sliced steak with cheese on top on a baking sheet under a broiler for 2-3 minutes and then building the sandwiches.