It is important to use untreated shrimp—those without added sodium or preservatives such as sodium tripolyphosphate—in this recipe; treated shrimp contain too much sodium and may have off-flavors. Most frozen E-Z peel shrimp have been treated (the ingredient list should tell you). We like the heat of a full teaspoon of pepper flakes; for a milder dish, use the lesser amount.
Toss shrimp and salt together in large bowl. Cover and refrigerate for 15 minutes.
Heat oil, garlic, and pepper flakes in 12-inch cast-iron skillet over medium-low heat until garlic is light golden brown, 8 to 10 minutes.
Add shrimp and cook until bottoms are light pink, about 2 minutes. Working quickly, flip shrimp and cook until just cooked through and pink all over, about 2 minutes longer. Off heat, stir in parsley. Serve immediately, directly from skillet, with crusty bread.
