Start by separating the heads and peeling and deveining the prawns. Place the prawn meat in a bowl and set aside.
In a large stockpot, add the prawn heads, shells, and tails. Add the water and ½ teaspoon of kosher salt. Bring the ingredients to a boil, then lower the heat and simmer for 20 minutes, stirring occasionally.
Strain the prawn stock out into a clean large pot and place on a back stove burner on low heat to keep warm. Discard the heads, shells, and tails.
In a large saucepan with high sides, heat the olive oil over medium heat. Add the onions, garlic, and celery, and stir, cooking for about 2 to 3 minutes, just until the vegetables become soft and translucent.
Turn the heat down to medium-low heat and add the rice to the saucepan with the vegetables and stir to coat the rice.
Add the wine, stir, and simmer until the wine is reduced, about 2 minutes.
Start a timer for 15 minutes. Ladle prawn stock one ladle at a time into the rice, stirring constantly in-between and allowing the rice to absorb the liquid before adding another ladle of stock. Repeat and continue until the timer goes off at 15 minutes.
Now add the prawns, stir them into the rice, and continue to ladle more stock in, stirring and cooking the prawns and allowing the rice to continue absorbing the stock. Do this until the prawns are cooked; the pink parts will have turned to a bright orange when cooked.
Remove the pan from the heat. Pour in the lemon juice and stir in gently. Drizzle olive oil over the pan and sprinkle chopped parsley. Serve immediately.
Notes
Prawns: You can usually find head-on, shelled raw shrimp at your local grocery store seafood & meat department. I buy mine at Costco. You can also buy shelled frozen shrimp without the heads, just be sure to thaw the shrimp overnight before using. The prawn stock will not be as flavorful without the shrimp heads, but it will still be enjoyable. Rice: The best rice to use for risotto is arborio rice. Arborio rice is a short grain rice with high starch content that's perfect for making creamy risotto. You can also use carnaroli rice or vialone nano rice. Or, in a pinch, you can use sushi rice. Wine: You can substitute chicken stock for the white wine.Storage: Allow the risotto to cool to room temperature then store in an airtight container in the refrigerator for up to three days.