Difford's Guide remains free-to-use thanks to the support of the brands in green above.
While the proportions on the classic Negroni are accepted as being equal parts with some boozehounds slightly upping the gin, the proportion on this amaro-dolce riff vary tremendously from equal parts to twice as much amaro to the other ingredients, to one-and-a-half parts gin to one part each of the other ingredients. Having tried them all (well, all we could find/come up with) we've settled on this 7:6:5 formula which is amaro-forward yet with assertive gin notes while not being overly sweet or boozy. However, you may prefer this recipe from Montenegro:
40 ml Amaro Montenegro
20 ml Gin
20 ml Sweet Vermouth
2 drops Angostura Bitters
Made with Rosso Antico in place of rosso (sweet) vermouth.