Grease 2 cookie sheets with butter. In 3-quart heavy saucepan, mix sugar, water and corn syrup. Cover; cook over medium heat 2 minutes. Cook uncovered over medium heat 25 to 30 minutes, stirring frequently, to 300°F on candy thermometer or until small amount of mixture dropped into cup of very cold water separates into hard, brittle threads. (Watch carefully so mixture does not burn.) Remove from heat. Add 2 tablespoons butter and the seasoned pumpkin seeds; stir until butter is melted. Immediately stir in baking soda.