Place the sugar cube (or 1/2 teaspoon loose sugar) in an Old Fashioned glass.
Wet it down with 2 or 3 dashes of Angostura bitters and a short splash of club soda.
Crush the sugar with a wooden muddler, chopstick, strong spoon, lipstick, cartridge case, whatever.
Rotate the glass so that the sugar grains and bitters give it a lining.
Add a large ice cube.
Pour in the Havana Club 7.
Serve with a stirring rod, and garnish with an orange slice if you're so inclined.