In a saucepan, melt butter.
Slowly add flour, stirring constantly to avoid lumps.
Cook 10-20 minutes (med-low heat). Roux should be smooth with an almond aroma.
Quickly remove from heat.
Put half and half in a thick bottom pot.
Heat nearly to boil.
Add roux to thicken, simmer 10 to 15 minutes.
Add brie, stirring constantly to melt.
Add fish base, strain and return to pot.
In a separate pot, cook oysters in their own juice.
Strain mixture into first pot, then add cooked oysters, juice and champagne to the mixture.
Add salt and white pepper to taste.
