Spray 8x8x2-inch square glass baking dish with vegetable oil spray. Bring broth and butter to boil in heavy medium saucepan. Gradually add cornmeal, whisking constantly. Whisk until mixture is very thick and starts pulling away from pan, about 6 minutes. Remove from heat. Stir in parsley and basil. Immediately transfer polenta to baking dish, spreading evenly. Cool 5 minutes, then cut polenta into 8 triangles; leave in baking dish. (Can be made 1 day ahead. Cover; chill. Rewarm in microwave oven on high, about 2 minutes.)
