Preheat the Blackstone grill over high heat (approximately 400 degrees Fahrenheit).
Place the diced potatoes in a bowl and the diced steak in a separate bowl. Pour 1 teaspoon of the oil into each bowl. Then season both with half of the garlic, beef rub and Italian seasoning. Toss each bowl separately with a large spoon to thoroughly coat the steak and potatoes with the oil and seasoning mixture.
Spread the remaining oil onto the Blackstone grill and spread it out with a spatula. Add the potatoes to the griddle and spread them in a single layer.
Squirt some water onto the potatoes and cover it with a dome or the lid on the Blackstone grill. Cook the potatoes for 4-5 minutes. Then toss the potatoes, squirt more water onto the potatoes, cover and cook for 4-5 more minutes.
Continue this process until the potatoes are fork tender. It took us three times for them to be fork tender, this will depend on how big you cut them, how hot your griddle is etc.
Then add the steak to the Blackstone grill. Let the steak sear for 2-3 minutes to brown the steak. Then toss the steak for 2-3 minutes until it’s cooked to the preference that you prefer.
Remove the lid from the potatoes.
Add the butter to the Blackstone grill in between the steak and potatoes.
Let the butter melt slightly and then toss the potatoes and steak with the butter to coat them with the butter mixture.
Remove from the grill. Serve immediately while warm and enjoy!