Partially freeze the Ribeye Steak for 20–30 minutes to firm it up, then thinly slice against the grain into very thin strips; season lightly with Kosher Salt and Black Pepper.
Peel and thinly slice the Yellow Onion.
Heat 1–2 tablespoons of Neutral Oil in a large skillet over medium heat; add the sliced onions and cook, stirring occasionally, until softened and golden, about 8–12 minutes. Remove the onions to a plate and keep warm.
Increase the skillet heat to medium-high and add a splash more oil if needed. Working in a single layer or small batches, add the sliced ribeye and spread it out so it sears quickly—cook undisturbed about 45–60 seconds, toss or flip, then cook another 30–45 seconds until browned but still juicy.
Return the cooked onions to the pan and toss with the seared beef; taste and adjust seasoning with additional salt and pepper as desired.
Warm the Cheez Whiz in a small saucepan over low heat or in short bursts in the microwave until it becomes pourable.
Slice the Italian Long Roll lengthwise (don’t cut all the way through) and toast the cut sides lightly in a dry pan or under the broiler until just crisp.
Pile the meat and onions into the toasted roll, spoon the warmed Cheez Whiz over the filling, close the sandwich, press lightly, and serve immediately.
