In a large heavy-bottomed pot, pour enough oil to reach a depth of 2 inches. Heat the oil until it reaches 375° on a deep-fry thermometer.
Over a medium bowl, sift together both flours. Stir in the salt.
In a separate bowl, beat together the whole milk, buttermilk and egg. Dip 1 clam at a time into the milk mixture, then dredge in the corn-flour mixture and drop it into the oil. Fry the clams in batches, turning occasionally, until the clams are golden brown and crisp, 40 seconds to 1 minute. Remove using a slotted spoon and transfer to a paper towel-lined plate to drain. Season with salt while still warm. Serve with tartar sauce and lemon wedges.