For the stock:
1 pound prawn heads and shells (about 8 cups), rinsed
4 quarts of cold water
½ medium onion, sliced
1 rib celery, cut crosswise into ¼ inch pieces
1 carrot, roughly chopped
For the risotto
7-8 cups prawn stock
1 ½ -2 pounds asparagus (approximately 24 spears), tough stems discarded and cut into 1-inch lengths
4 tablespoons olive oil
1 1/2 pounds spot prawns, heads and shells removed and reserved for stock
3 lemons, 2 zested and juiced and the third cut into wedges for garnish
Kosher salt (lemon salt if desired*)
1 large onion, diced
2 garlic cloves, minced
4 tablespoons butter
3 cups carnaroli rice
2 cup dry white wine
4 tablespoons unsalted butter
2 cups lightly packed grated parmesan cheese plus additional for garnish
freshly ground black pepper
Make the stock:
Rinse 8 cups spot prawn shells and heads and add to a 6-8 quart stock pot. Cover with 4 quarts cold water. Add the onion, celery, carrot and 2 teaspoons salt. Bring the stock to a simmer and simmer uncovered for 1 hour, taking care not to boil the stock. Strain the stock and let cool. The stock keeps for 3 days in the fridge or frozen in airtight containers for up to 2 months.
Make the risotto:
Heat to a simmer 7-8 cups of the prawn broth in a large saucepan. Add the asparagus and cook until al dente, 2 to 3 minutes. Transfer the asparagus to a bowl of ice and water.
Heat the olive oil in a 5 quart Dutch oven over medium heat. Add the shelled prawns, a splash of lemon juice, and a pinch of salt (lemon salt if using). Cook just until opaque and pink, about 1 to 2 minutes, depending on the size of the prawns. Transfer the prawns to a sheet pan and set aside
Add the diced onion to the Dutch oven and cook over medium heat until translucent. Add the garlic and cook, stirring for 30 seconds. Add the rice and cook, stirring, until the rice is translucent and every grain is coated with fat. Add the wine and simmer, stirring until all of the liquid is absorbed. Add 1 ladle of the prawn stock and cook, stirring, until the liquid is absorbed. Continue adding the stock, one ladle at a time, and cook, stirring, letting the liquid to be absorbed each time, until the rice is just tender (about 20 to 30 minutes). Stir in the cheese, the lemon zest, the remaining lemon juice, the butter, the asparagus, the prawns and their juice and salt and pepper to taste. Cover and let sit for 5 minutes before serving.
Spoon mounds of the risotto into pasta bowls and garnish each portion with a sprinkling of cheese and a lemon wedge.