Slice the polenta log into rounds. Pan-fry in a little oil over medium-high heat until golden and crisp on both sides. Set aside.
In butter, sear the mushrooms with the garlic until deeply browned.
Stir in the sage, then add cream, thyme, black pepper and a pinch of nutmeg. Simmer into a creamy sauce. Fold in the chestnuts if using.
Right before taking it off the heat, season with salt and stir in the parmesan for a sharp finish.
Spoon the creamy mushroom sauce over the pan-fried polenta rounds and garnish with chives.
Method reconstructed from the video (the caption lists ingredients only). The sauce is also delicious over pasta or poultry, or on a Thanksgiving plate. From HungryEmpire on Instagram.