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1
Put oven rack in middle position and preheat oven to 350u00b0F.
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2
Lightly beat together egg, milk, 1/2 teaspoon salt, and 1 teaspoon black pepper in a bowl. Whisk together flour, 1/2 teaspoon salt, and remaining teaspoon black pepper in a shallow baking dish. Whisk together cornmeal, remaining teaspoon salt, and cayenne in another shallow baking dish.
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3
Dredge 8 oysters in flour, knocking off excess, then dip into egg mixture, letting excess drip off, and dredge in cornmeal mixture, knocking off excess. Transfer to a large rack, then coat remaining oysters in batches of 6 to 8 in same manner, transferring to rack.
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4
Heat oil in a 4-quart pot over high heat until thermometer registers 375u00b0F.
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5
While oil is heating, halve bread crosswise, then cut each piece in half horizontally, cutting all the way through. Put bread halves back together and heat bread in oven (directly on oven rack) until warm, about 5 minutes.
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6
While bread is heating, gently drop one third of oysters into hot oil and fry, stirring occasionally, until golden, 45 seconds to 1 minute, then transfer to paper towels to drain. Fry remaining oysters in 2 batches in same manner, returning oil to 375u00b0F between batches.
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7
Spread mayonnaise on cut sides of bread, then make sandwiches, topping lettuce with oysters. Halve each sandwich crosswise for a total of 4 sandwiches.
