- Preheat the oven to 190C/375F, Gas Mark 5
- Brush each mushroom with a little olive oil and season with salt and pepper. Place on a baking sheet and bake for 10 minutes.
- Melt the butter in a saucepan. Stir in the flour and cook over a gentle heat for 1 minute. Remove from the heat and gradually beat in the milk a little at a time. Return to the heat and bring to the boil, stirring continuously, to give a thick sauce. Remove from the heat.
- Stir in the creme fraiche, mustard, crabmeat, spring onions and egg yolks. Season. Whisk the egg whites until stiff and carefully fold into the crab mixture.
- Spoon the mixture equally on top of each mushroom and bake for 12-15 minutes until puffed and golden. Serve immediately