1) Melt butter over low heat. Add shallots and dried red chilli flakes and saute until softened. Sprinkle in flour and cook until lightly coloured, roughly one 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 ten minutes.
2) Add the Brie, chives, salt and pepper, to taste, and stir until melted. Add Champagne.