A gizzard is made up of two muscles separated by a grinding plate that might have a yellow color. Slice gizzard in half along the plate and open it up. You'll find the grit and stones used by the bird to grind and digest their food.
Rinse off the grit and stones over a bowl of water so it doesn't clog up your drain.
Place the gizzards on a cutting board and use a knife to slice off the grinding plates and any other white or yellow membrane or silver skin so you are left with just the red meat that we'll use for frying.
Put the gizzards, chicken bouillon cubes and black pepper in a 6-quart Dutch oven and cover with water by a few inches. Bring to a boil over medium-high heat. Reduce heat to low, and simmer, covered, until gizzards are tender, about 2 hours. Remove from heat, and let stand, uncovered, until cool enough to handle, about 15 minutes.
Using tongs, transfer gizzards to the cutting board and pat dry with a paper towel.
Discard liquid remaining in the Dutch oven, and wash and dry the Dutch oven.
How to Fry Gizzards
Pour oil into the same Dutch oven to a depth of 2 inches and heat on stovetop to 375 degrees F using a candy thermometer.
While oil is heating, in a medium bowl, combine the flour, cornstarch, salt, garlic powder, onion powder and cayenne pepper until thoroughly mixed. Set aside.
Pour the buttermilk into another bowl large enough for the gizzards to be immersed in the buttermilk.
Prepare your dredging station. Place your gizzards in a bowl. Next to that, your bowl of buttermilk, and next to that, your dry mixture.
Take your gizzards, lightly dust them with your flour mixture, then dip them in the buttermilk until they are coated, and then place them in the flour mixture again. Be a little aggressive here and push the flour mixture into the wet gizzards. Make sure they are very thoroughly coated, or you will not achieve the crust and crunch you are looking for.
Gently place the gizzards in the hot oil and fry for until golden brown, about 2 to 3 minutes, stirring occasionally. Transfer to paper towels and sprinkle with a little salt. Serve immediately with your favorite dipping sauce.