Mince the prawns (2mm dice), onion and garlic (don't over-mince - it's nice to have some texture).
Heat the stock in a medium saucepan over low heat and keep at a low simmer.
In another saucepan, melt the butter over medium heat and cook the minced onion, garlic, prawn and thyme stirring occasionally, for 5-7 minutes, or until the onion is transparent. Add the rice and 2/3 of the lemon zest and stir until well coated.
Add the wine and stir constantly over medium heat until all the liquid has been absorbed. Now add the stock, half a cup at a time, until all the liquid has been absorbed and the rice is creamy and tender. This process will take up to half an hour.
Adjust the amount of lemon zest.
Remove from the heat and add most of the lemon juice and tarragon parsley. Season with salt and freshly ground black pepper, and adjust the lemon if necessary.