The District’s fourth Shake Shack opened last week in Union Station. As is customary, the burger joint introduced new concretes — the term it uses to describe its thicker-than-thick milk shakes — unique to that locale, often made with ingredients sourced from local purveyors ($4.25 single, $6.50 double). Here’s the scoop on the new options.

Busy Bee (above):

The only way to improve vanilla custard mixed with fresh strawberry puree? By adding a crumbled Bee Sting bar from Georgetown’s Baked & Wired. Made from shortbread, sliced almonds and honey, the baked good gives the concrete some bite.

Beaux-Arts Banana:

Vanilla custard is blended with bananas, caramel sauce and honey graham crackers from Pollystyle, a D.C.-based confection company. Five percent of sales from this concrete will go to Casey Trees, a local nonprofit that restores trees and promotes planting in the District.