Place a 10-inch cast iron skillet on oven's center rack. Turn oven to 400°F, allowing the pan to preheat.
In a medium bowl, whisk together cornmeal, flour, baking powder, baking soda, salt, and sugar. Set aside.
In a blender or combine buttermilk and frozen corn; mix until smooth. Add eggs and blend for a few seconds, just until combined.
Pour yogurt mixture and melted butter into cornmeal mixture. Fold ingredients together with a rubber spatula or wooden spoon until combined; don't over-mix.
With an oven mitt, remove preheated skillet. Add oil to hot skillet and swirl to coat bottom and sides of pan. Pour batter into skillet, scraping the bowl with a rubber spatula. Smooth top and place on the oven's center rack.
Bake for 25 minutes or until knife or toothpick comes out clean. Remove from oven and set aside to cool.
For the Cornbread Dressing
Once cornbread is cool, crumble into bite-size pieces (not too small) and spread in a single layer on a rimmed baking sheet. Bake in a 250˚F preheated oven for 1 hour until dry and lightly toasted (my preferred method). OR crumble cornbread, spread on a baking sheet and let stand uncovered overnight and up to 2 days to dry out.
Preheat oven to 350˚F.
Butter a 13x9x2-inch baking dish (3-quart) and set aside.
Place crumbled, toasted cornbread in a large bowl and set aside.
Melt butter in a large skillet over medium heat. Add onion and celery; cook and stir until softened but not browned, 8-10 minutes. Stir in sage, thyme, kosher salt and pepper; check for seasoning and add more salt and pepper to taste. Remove from heat.
In a medium bowl, whisk together eggs and chicken broth.
Add onion mixture and drizzle egg and broth mixture over cornbread; gently toss to combine. If mixture looks dry, moisten with stock as desired.
Transfer to prepared baking dish and spread into an even layer. (recipe note #1) Cover with foil and bake 30 minutes; remove foil and bake uncovered, 15 minutes more, or until golden brown and hot all the way through. Serve.
Notes
At this point you can tightly cover and freeze if desired for up to 1 month and bake from frozen, making sure it reaches an internal temperature of 165˚F before serving. You can also refrigerate after cooking for 3 to 4 days and reheat or freeze for up to 1 month. Reheat cooked dressing in a 350˚F oven, covered with foil for the first 25 to 30 minutes and then uncovered until hot all the way through with crispy edges, 10 to 15 minutes more.