Build in glass; add 2 of the 4 dashes of Angostura.
Add crushed ice to glass and swizzle.
Float 2 dashes of Angostura on top.
Serve with a straw and garnish with a sprig of mint.
Substitution Notes:
From trial and error, cachaça is a fine substitution for demerara rum. Do not use a strongly-charactered overproof like Wray and Nephew; it'll overpower everything else.