2) Take the pan off the heat and carefully pour in the brandy. Ignite the brandy with a long kitchen match and let it burn until the flame subsides. Return the pan to the heat, sprinkle in the flour, give it a stir, and cook for another 2 minutes.
3) Now add water to cover and deglaze, scraping up all the browned bits on the bottom of the pan with a wooden spoon. Add the cream and bring to a boil. Immediately turn the heat down to low and gently simmer until the soup is reduced and thickened, 30 to 45 minutes.
4) Strain the soup into a clean pan and season with salt and pepper. Chop the prawns. Return the bisque to a simmer, add the prawns and cook 2 to 3 minutes, just to cook the prawns through. Give the bisque a final taste for seasoning, pour it into warmed soup bowls and serve garnished with the orange zest and chives.