Add marinade ingredients to a large mixing bowl and whisk together. Add steak pieces to the marinade and use your hands to toss until coated. Set aside.
Place a large skillet over medium heat. Add 1 Tbsp olive oil and 1 Tbsp butter. Heat until butter is melted.
Add potatoes to skillet and stir to coat. Spread into an even layer and cook for 5 minutes.
Stir potatoes and continue to cook for another 15-20 minutes, stirring every 3-4 minutes, until the potatoes are fork-tender and crispy. Season with salt and pepper, stir the potatoes, and then transfer to a bowl.
To the same skillet, add 2 Tbsp butter, garlic, Italian seasoning, and red pepper flakes. Stir until butter is melted. Increase heat to medium-high.
Add steak pieces to the skillet. Cook for 6-8 minutes, stirring occasionally. The marinade and garlic butter will make a really yummy pan sauce.
At this point, you have 2 options for finishing up your meal.Option 1) Add the potatoes back to the skillet and toss in the pan sauce. Option 2) Plate the cooked steak and potatoes and spoon the pan sauce as desired over your meal.
Sprinkle with chopped parsley and serve immediately.
Notes
The potatoes can get a little soggy if you don’t serve them immediately after tossing in the sauce. My family prefers option 2.