In a large sauce pan, saute onion in olive oil until transparent.
Add cauliflower and cook on medium for 5-7 minutes stirring often.
Sprinkle flour over tender crisp cauliflower and then pour in chicken broth.
Add milk and cook until mixture begins to thicken.
Stir in thyme and brie and remove from heat. Stir until brie is melted and then add salt and pepper if desired.
Use an emersion blender to blend soup or transfer to a blender or food processor instead.
Garnish with green onions before serving.
To freeze: Cool completely. Pour into freezer containers, label and freeze up to four months. To serve: defrost overnight in the fridge. Warm in microwave or on stove top without letting soup come to a full boil.