Melt 2 T butter in a medium skillet. Add onion and saute over medium heat 1-2 minutes till translucent.
Add crabmeat and heat through. Add Brie, cover pan and removed from heat to soften cheese. Set aside.
in a medium saucepan, melt the remaining 2 T butter. Whisk in flour and salt and cook for 2 minutes. Heat the milk in a separate pan till just ready to boil.
Gradually add half the milk to the flour mixture, whisking till smooth.
Stir in remaining milk and heat mixture to boiling, stirring constantly. Allow to thicken 2 minutes and whisk in egg yolks.
Cook, whisking, for 2 more minutes and remove from heat.
Preheat oven to 375. Beat the whites with an electric mixer till stiff peaks form. Set aside.
Fold the crab mixture into the hot milk mixture. Gently fold in half the egg whites to lighten the mixture. Fold in remaining egg whites till just combined.
Butter 6 individual souffle cups (I used custard cups, which worked fine). Make souffle collars by cutting pieces of waxed paper or aluminum foil about 8 inches long each. Butter one side of each collar and wrap it around the top of the cup (you can tie string around this to hold it in place or tape the collar together after wrapping it around).
Divide the souffle mixture among the 6 cups. Bake for 20-25 minutes, or till puffed and golden brown and set in the middle.
Remove the collars and serve immediately with chive sauce on the side.
Heat lemon juice and creme fraiche till just warm (I did this in the microwave for about 1 minute). Stir in chopped chives.