Cook the broccoli as directed on the package; set aside. Meanwhile, melt the butter in a large saucepan over medium heat. Add the green onions and cook 2 minutes, stirring frequently. Stir in the stock and 1 cup of the milk. Heat the mixture to boiling. Whisk the flour into the remaining milk and add to the boiling liquid. Bring the mixture to a boil and cook 1 minute, stirring occasionally. Reduce the heat; add the salt, pepper, hot broccoli and cheese. Cook until the cheese is melted. Remove from the heat and stir in the sour cream.