Step 1

Heat half the oil in a large saucepan or stock pot over medium-high heat. Add the prawn heads and shells. Cook, stirring occasionally, for 10 mins or until shells change colour and caramelise. Transfer to a bowl and set aside.

Step 2

Add the remaining oil to pan. Cook the onion, fennel, carrot and garlic, stirring, for 8-10 mins or until soft and starting to brown. Stir in tomato paste. Return the prawn mixture to the pan with the sherry or wine. Cook for 3-4 mins or until sherry is reduced by half. Add 8 cups (2L) water, bay leaves and fennel seeds.

Step 3

Bring to the boil. Reduce heat to low and simmer, skimming the surface of any scum occasionally, for 2 hours or until reduced by a third. Remove from heat and allow to cool slightly. Strain through a fine mesh strainer into a large bowl.