Lightly muddle 5 fresh mint leaves in a little simple syrup or fresh cane juice or Steen's cane syrup or a sugar cube and a few drops of rum or a half tsp of turbinado (less refined, more tasty than white sugar) sugar until aromatic, Add 2oz rum and 1oz fresh squeeze lime juice, and some crushed ice. Shake briefly. Pour into tall glass, garnish with lime wedge and mint sprig if desired, and top up with Topo Chico if too much room is left in glass or you want more thirst quenching than mind expanding effect.