[tang-soo]

I remember White Castle when the burgers did not have the holes!

Then that would have been before my dad - lol. My understanding is the holes helps the burgers cook faster and allows the onion taste to permeate the burger better.

[grey_whiskers]

According to White Castle's old paper menus/serving tray liners, the holes help cook the patties by allowing the steam through.

[stars & stripes forever]

[the holes helps the burgers cook faster and allows the onion taste to permeate the burger better.]

Unfortunately there are more holes and onions than beef in the slider. To quote a competitor, “Where’s the beef?”

[MomwithHope]

That is BS - it saved them money on the meat so they did not have to raise the slider price.