Milk steak was an idea invented for the TV show It’s Always Sunny In Philadelphia, although the plotlines never revealed what it is or how it was cooked. However, some clever chefs have figured out how to make milk steak
I’d argue it’s neither a delicacy nor even a real thing
The Frankish Emperor Charlemagne, later in life, suffered from health problems from eating too much meat. His physicians told him that he should switch from roasted to boiled meat, which he chafed at. Having never boiled meat because I don't eat much meat, I assumed it was royalty having Royalty Problems™.
Looking at that, if it's a result of boiling, I'm starting to think instead that was cruel and unusual punishment by his doctors.
As someone who eats steak on rare occasion, if I was told I had to boil my steak from now on I would not be eating steak anymore. Boiled steak with no seat on the outside sounds awful.