If you start with the dry cornmeal, it is best to start this process at least a few hours ahead (ideally the night before) to allow the polenta to cool. Otherwise, feel free to cheat and buy the polenta tubes. If you use the tubes, simply skip the milk and broth in the recipe.
To make the polenta from scratch:
Soak the polenta in the milk (or broth). This can be done hours ahead or just prior to simmering the broth.
Next, bring the broth up to a boil. Reduce to a simmer over low heat. Slowly pour in the soaked polenta while stirring. Simmer over medium-low heat for about 15-25 minutes until the polenta is thick and starting to stick. Add a splash more broth or water if it is sticking, but not yet tender to the taste. In the end you will want a very thick polenta though.
Grease a baking dish with oil or line with parchment paper. Pour the polenta into the dish. Cool overnight until firm.
The next day…
Preheat the oven to 375.
Cut about two-thirds of the polenta in cubes and toss with a splash of the olive oil. Spread on a baking sheet and roast until crisp about 30-40 minutes.
If making this alongside the Herb Roast Turkey place half of the celery and onion in the bird and sprinkle several of the polenta cubes around the bird to absorb the juices and herb flavors. If not, all of these same ingredients can be sauteed in the next step.
Melt the butter or olive oil in a saucepan over medium-low heat. Add the onion and celery chunks. Sauté until they are tender and almost melting into each other. Stir in the remaining polenta chunks with a splash of broth (or juices from the bird). It will soften and almost melt into the vegetables. Add a bit more broth as needed.
When the turkey is roasted, remove the onions, celery and soaked polenta cubes.
Fold everything together including the roasted polenta cubes, buttery melted polenta, vegetables and fresh herbs. Place in a baking dish and if necessary warm in the oven at 350 until hot in the center.