Shake the pisco, passion fruit and lime juice with ice. Strain into a highball glass with ice. Fill with ginger ale and briefly, gently stir. Add a few drops of bitters to top. Garnish.
Passion fruit has ~3 to 4+% acidity, so if using unsweetened puree/juice, when combined with the lime, the drink can be quite tart compared to the standard Chilcano de Pisco. I found I could dial this tartness back into balance for our tastes by either upping ginger ale to 4 oz, or adding 1/4 oz of simple syrup.
Passion fruit (maracuyá) Chilcano recipes are one of many fruity variations of the Peruvian standard. This particular recipe is from Tamera Andersen, posted in July of 2017. It backs out some of the ginger ale in the base recipe to add passion fruit.