I had this cocktail at the launch of Shuck, an amazing amazing amazing new oyster bar in Borough Market (more on that later). Basically it's a Bloody Mary - which I LOVE - but with gin - also LOVE. Yes. Shuck use Gin Mare, which is that particularly botanical herbaceous gin I've mentioned before, and they emphasise this with the big stick of rosemary as garnish. I think there was also some fresh horseradish in here too, which was nice and hot but not 100% necessary if you're making at home.
You will need:
Pop it all in a shaker in your preferred quantities - we all like it differently, hold the worcestershire sauce for me - and away you go. This is definitely how I'll be drinking my Bloody Marys in future.
PS. They also had Bloody Marias which were tequila based...!