Greens with Polenta Croutons

Name: Greens with Polenta Croutons
Ingredients: Olive oil, for greasing the pan; Kosher salt; 1 cup instant polenta; 1 tablespoon unsalted butter; 1/2 cup grated cheese, such as Parmigiano-Reggiano; 1 tablespoon fresh rosemary, chopped; 2 tablespoons balsamic vinegar; 1 teaspoon Dijon mustard; Kosher salt and freshly ground black pepper; 1/4 cup extra-virgin olive oil; 10 cups (5 ounces) mixed baby greens; 1/2 cup cherry tomatoes, halved; 2 tablespoons dried cranberries or currants; 1/3 cup crumbled Roquefort cheese