Peel the prawns, leaving the tails on.
Remove the veins and set the prawns aside.
Boil the skins of the prawns in 200 ml water for 5 minutes, strain and reserve the stock.
Heat the stock, cream, 200 ml wine,saffron threads, a pinch of salt and freshly ground pepper in a saucepan and simmer gently until the sauce is reduced by half.
Cut half the butter into small pieces and whisk into the sauce.
Whisk in the sugar,then set aside.
Cook the linguine until al dente and drain.
While the pasta is cooking, heat a heavy-based pan over a medium heat.
Once the pan is hot,add half the remaining butter and half the garlic.
Stir for 30 seconds,then remove the garlic and discard.
Increase the heat to high and fry half of the prawns quickly until they turn pink.
Remove from the pan and repeat with the remaining butter,garlic and prawns.
Whisk the remaining wine and the lemon juice into the sauce and heat until hot.
Stir in the tomato.
Pour half the sauce over the pasta and stir to combine.
Carefully stir in the prawns,courgettes and the remaining sauce.