Preheat the oven to 400° F with the rack positioned in the centre of the oven. In a small bowl, mix 1 tablespoon of the sugar with the cornflour. Whisk in the egg yolks and set aside.

For the soufflé base, place the milk in a small Copper Core sauce pan over medium heat to warm. Melt the butter in another small sauce pan and heat over medium heat. Whisk the flour and a pinch of salt into the butter mixture. Whisk for about 30 seconds.

Remove from the heat, whisk in about 1/3 of the milk to form a smooth mixture without any lumps. Whisk in another 1/3 of the milk and then the final third. Return to medium heat and whisk, bringing to a simmer. Simmer for 30 seconds then remove the pan from the heat and immediately whisk in the chocolate to melt. Whisk in the egg yolk mixture. Place the base in a large mixing bowl.

Brush the Copper-Core butter warmer generously with softened butter. At the end, brush the butter vertically around the sides of the pan, so that the soufflé will rise along the lines. Coat the pan with granulated sugar. Whisk the egg whites in a large mixing bowl until they foam. Whisk in 1/3 of the remaining sugar until the whites begin to hold a form. Add another 1/3 of the sugar and continue to whisk to hold a bit more of a shape and then whisk in the remaining sugar until the whites are shiny and hold a firmer shape. Gently stir about 1/3 of the egg whites into the chocolate mixture to combine and lighten the batter. Fold the remaining whites into the batter.

Pipe or spoon the soufflé into the prepared butter warmer pan to reach to the top of the pan. Any extra can be placed in a ramekin and baked alongside the pot. Bake the soufflé for about 14 minutes or until it has risen and the top is set. Serve immediately.