1. Place the butter and chopped onion in a large microwave bowl and cook on High for 5 minutes. Stir in the chopped mushrooms, cover and continue to cook on high for 3 minutes.
2. Stir in the flour then gradually blend in the milk. Cover and microwave on high for 3 minutes.
3. Stir in the hot stock. Process to smooth in a blender.
4. Stir in the cream, taste and season. Pour back into the microwave bowl to re-heat. Cook on High for 2-3 minutes until hot.
based on a 600W oven