Recipe: Baked Polenta with Greens and Gruyère

Name: Recipe: Baked Polenta with Greens and Gruyère
Ingredients: 2 (12-ounce) bags frozen artichoke hearts; 2 tablespoons olive oil, plus more for the baking dish; 4 large bunches Swiss chard (about 3 pounds total), stems chopped into 1-inch pieces, leaves coarsely chopped and reserved separately; 1 teaspoon red pepper flakes; 6 cloves garlic, minced; 2 tablespoons red wine vinegar; Kosher salt; Freshly ground black pepper; 2 (18-ounce) tubes cooked polenta, sliced into 1/4-inch-thick rounds; 6 ounces grated Gruyère cheese (about 1 1/2 cups), divided; 1/2 cup grated Parmesan cheese