For the polenta:

1. Preheat oven to 375 degrees. Pierce holes in sweet potatoes using a fork. Place potatoes on a baking sheet and bake for 45-60 minutes, or until fork-tender. Let cool.
2. In the meantime, in a medium saucepan, bring 2 cups of water to a rapid boil. Add salt. While whisking, add corn meal to the water. Continue to whisk until polenta begins to thicken (about 1 minute).
3. Cover and cook for 30 minutes, stirring every 10 minutes or so.
4. Using a spoon, remove the flesh of the sweet potato and add to a food processor. Pulse until smooth texture.
5. Once polenta is done cooking, remove from heat and stir in the sweet potato until combined.
6. Pour polenta out onto a small baking sheet and use a spatula to spread out so that it’s evenly distributed (should come right up to edge of baking sheet). Refrigerate for about one hour or until set.
7. Preheat oven to 400 degrees and line another baking sheet with parchment paper.
8. Cut polenta into even squares (should make 32 squares) and transfer to the lined baking sheet.
9. Bake polenta squares for 30 minutes, flipping them over halfway through.

For the mushrooms:

1. In a medium saute pan, add olive oil over medium high heat. Add mushrooms and cook until they begin to caramelize (about 5 minutes).
2. Add garlic and cook for a couple minutes, until fragrant. Add thyme and cook for another minute. Add lemon juice. Once lemon juice has evaporated, add the wine, turn down the heat, and let simmer until it cooks off (about 10 minutes).
3. Top polenta squares with marinated mushrooms (about 2 mushroom quarters per square). Serve warm.