Slice squid tubes into 1cm-thick rings, leave tentacles whole. Place calamari in a bowl with the buttermilk until just covered. Salt and mix to coat evenly. Cover and refrigerate for at least 2 hours and up to 24 hours maximum.
Heat oil in a deep fryer, or a heavy-bottom, deep pan to 190°C, use a cooking thermometer to check this. While the oil is heating, combine all ingredients for the coating in a deep sided bowl.
Working in batches, drain calamari, allowing as much liquid to drip off as possible. Then transfer calamari into your coating mixture and toss to coat well. Make sure to separate the rings to ensure they are coated on the inside. Shake off any excess coating before frying. Gently place coated calamari into the heated oil and fry until lightly golden and crispy (30 seconds – 1 minute). Allow oil to return to temperature between batches so that your calamari become crispy.
Use a slotted spoon or metal tongs to remove calamari from hot oil. Drain on a wire rack with paper towels below to catch oil droppings. Sprinkle cooked calamari with additional OLD BAY Seasoning, if desired. Serve with fresh lemon and aioli.
Fresh calamari can be replaced with frozen crumbed calamari. Cook according to packet instructions, then toss with OLD BAY Seasoning after cooking.