Place the chicken between two pieces of plastic wrap and use a mallet or the bottom of a heavy skillet to pound each piece to a thickness of about ¼ inch.

In a medium bowl, mix the evaporated milk, 1 tablespoon of the pepper, and the garlic. Add the chicken pieces, cover, and refrigerate for 4 hours or up to overnight.

In another medium bowl, combine the 2 cups flour with 2 teaspoons of the salt and 2 teaspoons of the black pepper. Remove the chicken from the marinade (reserve the marinade). Lightly dredge the chicken pieces in the flour, shaking to remove the excess, dip them in the marinade, and then dredge them in the flour again. Set the chicken aside on a cooling rack or plate.

Fill a cast-iron skillet or other heavy-bottomed pot with vegetable oil to a depth of 1 inch, and heat it over medium-high heat to 350°F. Add a few pieces of the chicken to the pan and cook until browned on one side, about 3 minutes. While the chicken is cooking, continue to monitor the heat of the oil with a deep-frying thermometer, making sure the temperature stays between 330° and 350°F. Turn the chicken and cook on the other side for 3 to 4 minutes, until golden and cooked through. Remove the chicken from the pan and set it aside on a paper-towel-lined plate to drain. Repeat with the remaining chicken pieces.

Remove all but 2 tablespoons oil from the skillet, and add the onion. Cook over medium heat, stirring as needed and scraping up any browned bits in the pan, until the onion is soft and translucent, about 5 minutes. Add the remaining 2 tablespoons flour, stir well to combine, and cook for 2 minutes longer to make a roux. Whisk in the coffee and chicken stock, and cook until the sauce has thickened, about 6 minutes. Add the heavy cream, green onion, remaining 1 teaspoon pepper, and remaining 1/2 teaspoon salt, and cook for 2 to 3 minutes more, until the gravy reaches the desired consistency. If the sauce thickens too much, thin it with additional chicken stock.

To assemble: Slice a biscuit in half. Set a piece of fried chicken on the bottom half, spoon some of the gravy over the chicken, and top with the other half of the biscuit. Repeat with the remaining chicken, biscuits, and gravy. Serve immediately.