1.Preheat the oven to 200°C (180°C fan-forced). Grease a 2 litre (8-cup) capacity ovenproof souffle dish. Place the dish on an oven tray.
2.Add flour to a small stainless steel saucepan. Gradually whisk in milk, until a smooth paste. Cook flour mixture over medium heat, whisking constantly, until the mixture boils and thickens. Remove from heat. Stir in butter. Season with salt and pepper.
3.Whisk egg yolks and cheese into flour mixture. Transfer to large mixing bowl.
4.In a large bowl, beat egg whites with electric mixer, until soft peaks form. Fold egg whites into the cheese mixture, in two batches.
5.Pour mixture into the prepared dish. Bake 35-40 minutes, or until souffle is well risen and browned.
6.Meanwhile, arrange the salmon on a serving platter, top with the capers and the chervil. Serve souffle straight from the oven with the salmon.