Preheat the oven to 375°F /190°C. Grease 8 ramekins with butter.

Make a chocolate pastry cream: Chop the chocolate with a knife and place in a mixing bowl. Bring the milk to a boil in a saucepan. While it is heating, beat the egg yolks with the sugar in the bowl of a stand mixer fitted with a whisk until the mixture is pale. Incorporate the cornstarch. Pour one third of the boiling milk over the yolk-sugar mixture to heat it. Whisk well and pour in the remaining milk and whisk to combine. Return the liquid to the saucepan and bring to a boil. Remove from the heat. Stir in the chocolate until thoroughly combined. Allow to cool to room temperature.

Whisk the egg whites. With a flexible spatula, carefully fold them into the pastry cream. Divide the soufflé batter among the prepared ramekins and bake for 16 minutes. Chef’s note: Serve the chocolate soufflés with a scoop of ice cream.