Polenta Crackers with Roasted Wild Mushrooms

Name: Polenta Crackers with Roasted Wild Mushrooms
Ingredients: 3/4 cup all-purpose flour, plus more for dusting; 1/2 cup yellow cornmeal; 1/3 cup grated Parmesan; 3/4 teaspoon finely chopped fresh tarragon; Pinch cayenne; Kosher salt; 4 tablespoons cold unsalted butter, cut into 1/2-inch pieces; 1/4 cup heavy cream, plus more as needed; 1 pound mixed wild mushrooms such as shiitake, oyster and cremini, sliced; 3 tablespoons olive oil; Kosher salt and freshly ground black pepper; 1 tablespoon fresh lemon juice; 1 tablespoon chopped fresh tarragon