The hush-hush speakeasy-inspired bar The Doctor’s Office on Capitol Hill has the perfect prescription after a sweaty, sticky day: a crisp, citrusy vesper that’s served so bone chillingly cold that the glass flask it was poured from was frosty. Upon taking a few sips of one when the bar debuted in February 2020, I turned to then-bar manager Keith Waldbauer to say, “This is so good.” “It better be,” he quipped. The Doctor’s Office bar team tested 300 different versions of the vesper to get the right gin-vodka combo and the ideal water dilution level, he said. I must have ordered this classic a zillion times over the past six years because after I bellied up to the bar one evening, the barman asked, “The usual?” My “usual” should be your go-to cocktail for your next house party. You don’t even need any bar equipment since the most crucial tool for making this great vesper is … your freezer. You might even have two crucial ingredients already at home: vodka and gin. Martinis are trendy now in restaurants.…