Step 1

Put the shrimp shells and tails, 3 cloves of garlic, 1 teaspoon salt and 1/2 teaspoon pepper in a medium saucepan. Cover with 7 cups of water and bring the mixture to a boil over medium-high heat, then reduce the heat to low and simmer for 20 minutes.

Step 2

Strain the shrimp broth into a large liquid measuring cup. Discard the shells and garlic. You should be left with 6 cups of broth. If the broth reduced more, just supplement with a little extra water to yield 6 cups. Add the broth back into the empty saucepan and keep warm over low heat.

Step 3

Heat a large straight-sided skillet or braiser over medium-high heat. Heat 1 tablespoon of oil until shimmering. Add the chopped shrimp and sprinkle with a generous pinch of salt and pepper. Cook, stirring occasionally, until the shrimp are pink, about 5 minutes. Meanwhile, thinly slice the remaining 3 cloves of garlic and set aside. Transfer the cooked shrimp to a plate and set aside.

Step 4

Reduce the heat to medium low and add 1 tablespoon of oil if the skillet is too dry, then add the sliced garlic. Cook, stirring frequently, until fragrant and just starting to soften, about 1 minute. Stir in the arborio rice until coated with the oil. Add the lemon juice and cook, stirring occasionally, until it has been mostly absorbed, about 2 minutes.

Step 5

Ladle 1 cup of the warm stock into the rice and cook, stirring gently without stopping, until the rice has absorbed the liquid, 2 to 3 minutes; you will know it's time to add more stock when you move the rice aside and no liquid pools in the center.

Step 6

Repeat this process, adding more stock a ladleful at a time, until the rice is al dente and creamy, 20 to 25 minutes. If you run out of broth before the risotto is at its desired doneness, add some water.

Step 7

Stir in the arugula, shrimp and half of the lemon zest and cook until the arugula wilts slightly.

Step 8

Serve topped with the remaining lemon zest.