- 4 pounds prepared polenta, sliced into 1/2-inch-thick rounds (about 30 rounds)
- 2 tablespoons extra-virgin olive oil, plus more for brushing
- 1/4 cup (1/2 stick) unsalted butter
- 2 pounds assorted wild mushrooms (such as oyster, crimini, and/or stemmed shiitake), cut into thick slices
- 2 shallots, thinly sliced
- 1/4 cup Sherry vinegar
- 1 3/4 teaspoons kosher salt
- 1/2 teaspoon freshly ground black pepper
- 1/2 teaspoon crushed red pepper flakes
- 1/2 cup chopped parsley leaves
- 4 ounces Fontina cheese, coarsely grated (about 1 cup)
- Preheat oven to 450°F. Brush both sides of polenta slices very lightly with oil and arrange on 2 rimmed baking sheets. Roast polenta until lightly golden brown and warmed through, about 25 minutes.
- Meanwhile, melt butter with remaining 2 Tbsp. oil in large, deep skillet over medium-high heat. Add mushrooms and cook, stirring often, until tender and browned, about 12 minutes. Add shallots, vinegar, salt, black pepper, and red pepper and cook, stirring, until tender, about 5 minutes. Stir in parsley.
- Divide mushroom mixture between baking sheets with polenta. Top with cheese. Continue to roast until cheese is melted, about 5 minutes.
- Arrange polenta bites on a platter and serve.