Shake Shack + Cake Love = Red Velvet Concrete.

By new DCist Food and Drink Contributor Erin Zimmer As legend has it, when a Waldorf-Astoria guest back in the 1940s forcefully requested the hotel’s secret red velvet cake recipe, the hotel gave it to her—along with a hefty bill for the prized information. The miffed guest, whose lawyer supposedly advised her that she had to pay, apparently took revenge by spreading the recipe everywhere she could. Whether the Waldorf-Astoria tale is real or no…