If your prawns have the head and shell on, remove them and place them in a small 17cm (7") saucepan with the fish stock. Gently heat it over a low-medium heat whilst you prepare the remaining ingredients.If not, don't worry!
Have a taste of the stock and season with salt as needed.
Roughly chop all but 6 of the prawns; we will use these as garnish later.
Dice the celery as finely as you can.
Cut the shallot in half, peel it, then dice it as finely as you can.
Peel and dice the garlic cloves as small as you can.
Remove the stem and seeds from the chilli pepper and dice it as small as you can.
Zest the lemon and cut it in half.
Heat a wide-based 28cm or 11" frying pan over a medium heat and add the olive oil. When the oil is hot, add the celery and shallots and cook without colouring for 4-5 minutes.
Add the garlic and half of the chilli, stir for 30 seconds, then add the rice. Stir continuously for 2-3 minutes. The edges of the rice should become opaque.
Add the white wine and stir until almost all of the wine has evaporated or absorbed. You should end up with an almost milky residue in the base of the pan.
Add a ladle of the hot fish stock (strained of the shells if you used them) and stir again until almost all of the stock has been absorbed and you have a similar white starchy residue in the base of the pan.
Repeat this process until the rice is very nearly cooked, and when you have just 1 ladle of the stock to go in, add the chopped prawns and squeeze in the lemon juice. Again, stir continuously whilst this last bit of stock cooks out, and you have a nice wet risotto.
Remove the pan from the heat and cover it with a lid or some foil, and allow it to sit for 3-4 minutes.
Whilst the risotto is resting, heat a small 20cm or 8" frying pan over a medium-high heat and add the butter. When the butter begins to foam, add the prawns, lemon zest, the remaining chilli, parsley and a pinch of salt and saute for 2-3 minutes.
Serve the risotto in the bowl, add the prawns and drizzle with the butter mix.