Preheat oven to 425 degrees. Line a large baking sheet with parchment.
Whisk together the cider, maple syrup, soy sauce, bourbon (if using), cayenne pepper, and a pinch of salt and pepper. Pour half of the sauce over the salmon filets. Let sit 10 minutes.
Toss the apples and Brussels sprouts in 1 tablespoon of olive oil, and a big pinch of salt and pepper. Spread onto the baking sheet. Roast 12 minutes.
Pour the reserved marinade into a small saucepan and bring to a boil for 8-10 minutes or until the sauce is reduced by half and coats the back of a spoon. It will continue to thicken as it cools.
Push the sprouts and apples to one side of the baking sheet. Set the salmon on the baking sheet (discard the marinade the salmon soaked in). Bake an additional 10-15 minutes until desired doneness.
To make the polenta, melt the butter in a large skillet until slightly browned, about 3-4 minutes. Pour in the milk and 1 1/2 cups of water. Bring to a simmer, then pour in the polenta. Stir constantly for about 5 minutes until thickened. Remove from the heat and stir in the parmesan, honey, and a pinch of salt and pepper.
Divide the polenta, salmon, Brussels sprouts, and apples into bowls or plates. Drizzle with the cider reduction. Enjoy that shit!