I'll include both the full bottled proportion and a single-serving recipe below.
16 oz (2 oz) amber rum (Appleton VX)
6 oz (3/4 oz) blended scotch (Famous Grouse)
6 oz (3/4 oz) sweet vermouth (Cocchi Torino)
2 oz (1/4 oz) amontillado sherry
2 oz (1/4 oz) Casoni 1814 (Aperol or Cappelletti would work too)
8 oz water (omit for single-serving)
For the bottled version, combine everything and keep refrigerated until ready to serve, then add to a pitcher with several large ice cubes. For the single-size version, stir and strain over a large cube in an old-fashioned glass.