Melt butter over low heat. Add shallots and red pepper flakes and saute until softened. Sprinkle in flour and cook until lightly colored, roughly 1 minute. Gradually whisk in the stock and cream. Increase heat to medium-high and bring to a boil; reduce to medium-low and simmer for 10 minutes. Add the Brie, chives, salt and pepper, to taste, and stir until melted. Add Champagne. Add the oysters and cook for 3 minutes.