1 1/2 pounds cleaned calamari, bodies cut into 1/2-inch rings and tentacles left whole
2 cups well-shaken buttermilk
3 cups all-purpose flour
2 tablespoons kosher salt
Canola oil, for frying
1 lemon, cut into 8 wedges
Place calamari in a medium nonreactive bowl, cover with buttermilk, and marinate in the refrigerator for 1 hour.
Heat the oven to 200°F and arrange a rack in the middle. Line a baking sheet with a few layers of paper towels.
Combine flour and salt in a large bowl and whisk to aerate and break up any lumps; set aside.
Pour 2 inches of the canola oil into a Dutch oven or a large, heavy-bottomed pot. Heat over high heat until the oil reaches 400°F on a deep-frying/candy thermometer. Remove a handful of the calamari from the buttermilk, place it in the flour mixture, and toss to evenly coat. Transfer calamari to a fine mesh strainer and gently shake any excess flour back into the bowl. Carefully place the calamari in the oil and fry until light golden brown, about 1 minute. Transfer to the prepared baking sheet using a slotted spoon, and season with salt and freshly ground black pepper. Place the baking sheet in the oven to keep warm.
Return the oil to 400°F and repeat the process with the remaining calamari (about 5 to 6 batches total). Serve with lemon wedges.