Combine milk and 1 teaspoon kosher salt (use hald for table salt) in a bowl, the soak the squid rings in the mixture. Cover and refrigerate for about an hour.
Combine all-purpose flour, rice flour, and baking powder in a separate bowl.
Drain the squid and transfer them to the flour mixture. Coat them evenly and shake off any excess flour.
Set a small, wide-mouthed pot over high heat, then add an inch of oil. Dip a wooden spoon handle or chopstick to check when it's hot and ready—it should steadily bubble around it. If using a thermometer, aim for 375° F (190° C).PRO TIP: The oil needs to be very hot before dropping in the squid. This high temperature browns and crisps the squid quickly without overcooking.
Fry the calamari in batches until they're golden brown, which should take about 2-3 minutes. Gently stir them to keep them from sticking together. Make sure to let the oil heat back up to a high temperature between batches for even cooking. Don't overcrowd the calamari when frying to avoid a temperature drop which can make them greasy and soggy.
Use a spider or slotted spoon to quickly remove the batch from the oil.
Lay them out on paper towels to soak up any extra oil. Sprinkle a bit more salt on them while they're still hot.
Serve with lemon wedges and pair them with dipping sauces like sweet chili sauce or spiced vinegar. Marinara sauce and aioli are also popular choices.
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Notes
Squid: Go for small to medium-sized squid since they're usually sweeter and more tender. Cut them into thick rings so the coating gets nicely browned and crunchy without overcooking the squid.
Milk: You can use whole milk or other milk products like buttermilk or yogurt diluted with water. They help tenderize the squid, cut any fishy smell, and make sure the coating sticks.
Flour: A combination of all-purpose flour and rice flour makes the crunchiest, golden-brown coating without being too heavy. If you don't have rice flour, potato starch or cornstarch are good substitutes.
Baking powder: This is the secret to a light and airy coating. It adds little bubbles that make all the difference, so don't skip it.