Trim, rinse and thoroughly dry the green beans. Put them in a medium bowl and toss with the buttermilk to coat.
Combine the flour, cornmeal, baking powder, salt and cayenne in a large bowl or resealable plastic bag. Drain the green beans and toss them in the flour mixture to coat thoroughly.
Bring about 1/2-inch of oil in a wide, heavy pot to 350 to 375 degrees F over high heat. Prepare a cooling rack set over paper towels.
Adjust the heat to maintain that temperature range. Test the temperature by using a thermometer or by dipping the handle of a wooden spoon into the oil. If the oil bubbles around the handle, it is hot enough to fry the beans.
Shake excess flour mixture off the beans as you add enough of them to form a single layer in the oil. Fry until golden- to medium-brown and beans are tender, about 3 minutes. Transfer with tongs or a slotted spoon to the prepared cooling rack and sprinkle with salt. Repeat with the remaining beans and serve hot.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.