Method

• 1.
  Heat 2 tbs oil and butter in a large saucepan over medium heat. Add half the fennel and half the garlic, and cook, stirring, for 6 minutes or until softened. Add the tomato paste and cook, stirring, for 2 minutes, to lightly caramelise. Add the prawn heads and shells and cook, stirring, for 8 minutes until coloured. Stir 1 punnet tomato into the prawn mixture. Add 11/2 cups (375ml) water and 2 thyme sprigs and bring to a simmer. Reduce heat to low and cook for 25 minutes, pressing down the prawn heads and tomato to extract as much flavour as possible. Strain through a fine sieve to extract all of the liquid. Set aside. Discard solids.

• 2.
  Heat remaining 2 tbs oil in saucepan over medium heat and add remaining fennel and garlic, and fennel seeds. Cook, stirring, for 6 minutes or until softened. Add remaining tomato and cook for 5 minutes, stirring gently.
• 3.
  Meanwhile, cook pasta in boiling salted water according to packet instructions.
• 4.
  Add prawn stock and remaining lemon thyme sprigs to saucepan with fennel and garlic mixture. Bring back to a simmer and cook for 10 minutes until tomato skins start to burst. Add the prawn and cook for 2 minutes or until just cooked through and stir through the lemon zest and juice. Season to taste. Fold pasta through sauce then divide among serving bowls. Scatter over lemon thyme leaves to serve.