For the whole grain buttermilk cornbread: Preheat the oven to 450 degrees F. Place the fat in a 10 1/2-inch cast-iron skillet or ovenproof baking dish and heat in the oven until sizzling, about 10 minutes.
Meanwhile, in a bowl, combine the cornmeal, baking soda and salt. In a large measuring cup, combine the buttermilk and egg. Add the buttermilk combination to the cornmeal mixture and stir to combine.
Remove the heated skillet from the oven and carefully pour the hot fat into the batter. Stir to combine, and then pour the batter back into the hot skillet. Bake until golden brown and a toothpick inserted in the center of the bread comes out clean, 20 to 25 minutes. Remove to a rack to cool slightly. Cut with a serrated knife just before serving.
For the collard greens: While the cornbread is baking, stack several collard leaves at a time and cut into 1/4-inch strips; repeat until all the leaves are shredded.
Heat the oil in a large pot over medium heat. Add the onions and cook until clear and translucent, 3 to 5 minutes. Add the garlic and cook until fragrant, 45 to 60 seconds. Add the greens, stock, vinegar, red pepper flakes, bay leaf and turkey; season with salt and pepper. Increase the heat to medium high and bring to a boil. Reduce the heat to medium low, cover and cook until the greens are just tender, 15 to 20 minutes. Taste and adjust for seasoning with salt and pepper. If desired, shred the meat off the turkey drumstick to serve with the collards.
Serve immediately with hot buttered cornbread.
Look for cornmeal that is whole grain and not de-germinated. Look for stone-ground artisan meal or a national brand such as Bob's Red Mill. The cornbread keeps in an airtight container for up to 3 days.