1. For the polenta: Preheat oven to 350F.
2. Peel and chop onion.
3. In a Dutch oven, heat half of the olive oil over medium heat. Add the onion and sea salt and cook until the onions begin to soften.
4. Reduce the heat to low, add the garlic, and sauté for a couple more minutes.
5. Add the chicken broth, and bring to a boil over medium/high heat.
6. Slowly add the cornmeal while continually whisking until completely combined. Cover the pot and place it in the oven. Bake for 35 - 40 minutes, stirring occasionally.
7. Remove from the oven and stir in the remaining olive oil. Season with salt and pepper to taste.
8. Transfer polenta mixture to a greased glass or ceramic pie or tart pan, and spread evenly and set aside.
9. For the mushroom sauce: Roughly chop celery. Peel and roughly chop carrot. Peel onions and roughly chop a little under half of them.
10. Add chopped veggies to a saucepan with filtered water, a bay leaf, and dried porcini mushrooms. Bring to a boil, then lower to a simmer and cook for 20 - 30 minutes; strain.
11. Finely chop the rehydrated porcini mushrooms. Clean and slice any large fresh mushrooms, leaving smaller mushrooms whole if desired.
12. Dice the remaining onion, chop parsley, and mince sage and thyme.
13. In a large skillet, heat half of the olive oil over medium high heat. Add diced onion and sea salt to the hot oil; cook until translucent.
14. Lower the heat to medium, season the onions with a generous pinch of sea salt and a few grinds of black pepper, and continue stirring until caramelized, about 5 minutes.
15. Remove the onion to a small bowl.
16. Return the pan to the heat, add the remaining olive oil, and turn the heat to high.
17. Add mushrooms, stirring well to coat with oil. Keep the heat high and sauté mushrooms until they brown lightly. If juices accumulate in the pan, pour them off and reserve.
18. Add garlic, thyme, sage, and pepper flakes; stir well. Reduce the heat to medium, add the caramelized onions and the tomato paste, and stir to combine.
19. Cook for another 2 minutes, stirring.
20. Mix arrowroot and filtered water in a small cup until completely combined to make slurry. Slowly pour hot broth over the mixture.
21. Stir in slurry and let the ragout cook for another 5 minutes. If it’s too thin, cook it a bit longer; if too thick, add a bit more broth.
22. Adjust with sea salt and freshly ground pepper to taste.
23. Top with mushroom sauce and reheat in the oven until bubbly and warm and serve.