How do you brew the swelling solution from harry potter?

Part 1:

  1. Add 2 scoops of dried nettles to the mortar
  1. Add 3 pufferfish eyes to the mortar
  1. Crush to a medium fine powder
  1. Add 2 measures of crushed mixture to your cauldron
  1. Heat on a medium temperature for 20 seconds
  1. Wave your wand
  1. Leave to brew and return in 45-60 minutes.

Part 2:

  1. Add 1 bat spleen to your cauldron
  1. Stir 4 times, anti-clockwise
  1. Heat to low for 30 seconds
  1. Wave your wand to complete the potion.
-Pottermore Wiki