In a large saucepan, melt butter over medium heat. Stir in flour until smooth; gradually whisk in stock and cream. Bring to a boil, stirring constantly; cook and stir until thickened, 4-5 minutes. Stir in cheese, pumpkin and seasonings until cheese is melted. Serve with tortilla chips and if desired, sprinkle with pumpkin seeds and cilantro.