It is the kümmelweck-style of Kaiser roll (the author here wrongly spells it "kimmelweck", a German word) that needs to be not less than four inches diameter to hold enough beef to make it satisfying. Five would be better.
Without the roll, it's only a sandwich.
I came to be accustomed to a broad exposure to marvelous cuisine as a born-again native of Western New York, a Southern Tiersman that resided and worked in the Buffalo-Niagara-Lewiston area for four and a half years. I found no better steaks anywhere else in the world, including Texas, Kansas, Colorado, or Tokyo. Buffalo had the best tender, rare roast beef for the sandwiches any where else.
Arby's® Restaurants have been very successful im multiplying since the 1960s by making beef-on-a-roll (and other tasty items) like it, but their beef is not on the big kümmelweck roll, which elevates this item to a heavenly plane! (More caraway seeds would be even better for the Kaiser rolls in the above image.)