Heat your stock to a simmer and keep it hot in a pot on the stove. Remove 1 cup of the hot stock and place it in a bowl with the saffron. Set this aside to infuse.
Heat the olive oil in a medium-sized heavy-based pot, and gently cook the onion and fennel for about 5 minutes until it softens and becomes translucent. You do not want it to take on any colour. Add the rice and cook it for a few minutes until the grains are glossy and they just start to make a crackling sound.
Add the wine and allow this to bubble and absorb. This will happen quite quickly. You will now cook the risotto over a medium heat.
Start adding ladles of hot stock to the rice and stir constantly until it is absorbed. Repeat this for amount 15 minutes, then add the saffron-infused stock and watch the colour turn a vibrant yellow.
Carry on cooking the risotto until it is al dente, and ensure there is still a lot of liquid. Add the butter to the pot and stir to emulsify it.
At this final stage, heat a non-stick frying pan over a medium heat and then add the butter. Just as the butter starts to melt and bubble, add the prawns and quickly cook them on both sides until their flesh has turned pink and they have curled up.
Serve the risotto with the prawns on top and drizzle with any remaining brown butter from the pan. Trust me on this.