Preheat oven to 200C/400F/Gas 6.
Place a baking sheet in the oven to preheat.
Grease two ramekins with butter and set aside.
Melt the butter in a small saucepan over a medium heat. Add the flour and stir to form a thick paste or roux. Cook for one minute then remove from the heat.
Gradually add the milk, whisking continuously, until a thick and smooth sauce is formed.
Mix the egg yolk, chocolate and maple syrup together in a separate bowl.
Gradually add the white sauce to the chocolate mixture, stirring constantly.
Carefully fold the egg whites into the chocolate mixture, then fill the two ramekins with the soufflé mixture. Run a thumbnail or teaspoon handle around the inside edge of the ramekins.
Place the ramekins onto the preheated baking sheet and bake for 8-10 minutes, until the soufflés have risen.
To serve, place each soufflé onto the centre of a plate, dust with icing sugar and drizzle with maple syrup.