Rinse the cleaned crabs and pat them completely dry with paper towels. Place them in a shallow dish and cover with buttermilk. Let soak for at least 10 minutes.

In a separate shallow dish, whisk together the flour, cornstarch, Old Bay Seasoning, kosher salt, black pepper, and cayenne pepper.

Heat about 1.5 inches of oil in a heavy-bottomed pot to 360°F (182°C).

Lift one crab at a time from the buttermilk, let the excess drip off, and dredge thoroughly in the flour mixture, pressing lightly to coat. Shake off any excess.

Carefully place 2-3 crabs in the hot oil. Fry for 2-3 minutes per side, until deep golden brown and crispy.

Remove the crabs from the oil and drain them on a wire rack. Immediately sprinkle with a little extra salt or Old Bay.

Repeat with the remaining crabs, allowing the oil to return to temperature between batches.

Serve immediately with lemon wedges and a sprinkle of fresh parsley.