Wanted to try this but I tend not to keep sweet vermouth in the house since I have trouble using it up. Eventually settled on a 2:1:1 ratio of gin, creme de cacao, and fresh lemon juice, and then added in a half each of dry white wine and grand ma, together with a tsp of sugar syrup, to try and fill in for the vermouth. I don't think the substitution is especially accurate, but I did enjoy the drink, which came together like a gimlet with additional aromatic complexity from the chocolate