Food Network teaches how to crush, slice and mince garlic. Peel off some of the papery skin from the garlic and then smash the head of garlic with the heel of your hand to loosen the cloves; if you only need a few cloves, leave the head intact and pull some off. Separate the cloves. To peel a clove, cut away the root end with your knife. Lay the flat side of the knife over the clove while holding the knife handle, then with the heel of your free hand carefully whack the knife against the garlic to separate the skin from the clove. To crush the peeled garlic, lay the flat side of the knife over the clove and smash it again. To slice peeled garlic, lay the clove flat on the cutting board and hold it with the fingertips of one hand, keeping them curled under. Using a rocking motion with the knife, make thin slices by moving the knife slowly across the clove. To mince peeled garlic, lay the flat side of a knife over the clove and smash it. Roughly chop the clove then move your free hand flat across the tip of the knife and use a rocking motion to chop the garlic until it’s finely minced.
In a bowl, combine the garlic, zest and juice of 1 lemon, olive oil, red pepper flakes, salt and pepper, to taste, and the shrimp. Set aside.
Meanwhile make a quick shrimp stock: In a small pot, over medium heat, add the shrimp shells and onion. Cover with water and bring to a boil. Reduce the heat and simmer for 20 minutes. Strain into a bowl and discard the shells and the onion.
Bring a large pot of water to a boil over high heat and add a generous amount of salt. Add the linguini and cook until just tender, 2 minutes less than instructed on the package. Drain and reserve 1/2 cup of cooking water.
Heat a skillet over high heat. Add the shrimp and cook until they turn pink and start to caramelize, about 3 minutes. Remove the shrimp from the pan to a plate and add the remaining marinade. Let cook a few minutes then add about 1 cup of shrimp stock and about 1/2 cup pasta water. Continue to cook until sauce reduces by half. Add the zest and juice of the remaining lemon, the butter and the parsley and stir to combine. Adjust seasoning with salt and pepper, to taste. Add in the shrimp and pasta and toss to combine with the sauce. Turn out into a serving bowl and serve immediately.