This recipe uses a classic caramel sauce. It will set up in the fridge, but can be easily warmed and re-warmed as needed.
Preheat the oven to 400ºF (200 ºC). Lightly butter six 1-cup (250 mL) soufflé or other similar volume, straight-sided baking dishes. Sprinkle the inside of the cups with sugar and tap out any excess. Place the dishes onto a baking tray and chill until ready to fill and bake.
Whisk the milk, 4 Tbsp (50 g) of the sugar, the cornstarch and vanilla in a small dish and set aside. Melt the chocolate and butter in a small saucepot over low heat, stirring constantly until melted. Stir in the milk mixture in 2 additions, whisking until evenly blended (the mixture will be a thick paste and may look a little grainy, but that is to be expected – it will smooth out after the whites are folded in.) Keep this warm while preparing the egg whites. Alternately, this mixture can be prepared in advance and chilled, then re-warmed over low heat when ready to bake the soufflés. When ready to move to step 3, transfer the warm chocolate to a large bowl.
Whip the egg whites in a stand mixer fitted with the whip attachment or using electric beaters on high speed until they are foamy then slowly pour in the remaining 6 Tbsp (75 g) of sugar and continue to whip until the whites hold a soft peak when the beaters are lifted. Fold in a third of the whites into the warm chocolate and quickly but gently fold them in – they will deflate quite a bit, but this is expected. Fold in the remaining two thirds of the batter until incorporated then pour this into the prepared soufflé dishes.
Bake the soufflés for 15-18 minutes until the tops take on a dull look, (they will rise well above the top of the soufflé dishes.) Serve immediately with caramel sauce (recipe follows) on the side (each guest can make an opening in the top of their soufflé and pour the caramel sauce in.)
Place the water, sugar and corn syrup (or lemon juice) in a medium saucepot and have the cream and butter measured and on hand. Bring the sugar up to a full boil on high heat without stirring and continue to boil, occasionally brushing down the sides of the pot with water, until the sugar turns a light amber colour, about 5 minutes. Remove the pot from the heat and whisk in the cream and butter, watching out for the steam and bubbling. Once the bubbling subsides, add the vanilla and salt. Cool to room temperature and then chill until ready to use (the sauce should be re-warmed over medium heat to use.)