Build in a Collins glass, fill with crush ice, and swizzle to mix and chill. Top with more crushed ice, garnish with mint sprigs and 5-6 dash Angostura Bitters, and add a straw.
Back in 2014, Swizzles were all the rage here in Boston especially given the first Death & Co. cocktail book and the fact that we had a D&Co. alumni at the Hawthorne putting them on the menu (and it radiated out to other bars). One of the drinks and flavor combinations that I was still thinking about was Mike Fleming's Sinnerman at West Bridge; the simple combination of sweet vermouth, gentian liqueur, and allspice dram made for a rather good aperitif. I did find it a touch sweet and figured that some citrus would dry it out a little. Or if I added some citrus and made a Swizzle out of it...