Butter a shallow 2-quart (2-l) baking dish

Set a large bowl over a pan of barely simmering water (do not let the bottom of the bowl touch the water). Melt the butter in the bowl. Add the chocolate and coffee and stir gently until the chocolate has melted and the mixture is smooth. Remove from the heat and set aside.

In a medium bowl, mix together the cornstarch and 1/4 cup (60ml) of the cold milk until the cornstarch has dissolved. Add the egg yolks and whisk until smooth.

In a medium saucepan, combine the 1-3/4 cups (420ml) milk, t tablespoons of the sugar, and the salt and heat over medium-high heat until the mixture is warm.While stirring continuously with a whisk, gradually pour the milk mixture into the yolks. Scrape the milk and warmed yolks back into the saucepan and cook over medium high heat, stirring continuously with the whisk, until the mixture comes to a boil.

Reduce the heat slightly and continue to stir with a whisk until thick and shiny, 15 to 30 seconds. Remove from the heat and scrape the mixture into the bowl of melted chocolate; stir until smooth. Let sit until it’s just slightly warm. Add vanilla extract if using.

Preheat the oven to 375 degrees F (190C) with a rack in the center position.

In the bowl of a stand mixer fitted with the wire whisk, or by hand in a medium bowl, whisk the egg whites on medium speed until frothy. Increase the speed to high and when the egg whites start holding their shape, whisk in the remaining 3 tablespoons sugar,1 tablespoon at a time.

Fold one-third of the egg whites into the chocolate mixture, then fold in the remaining egg whites just until no streaks of whites are visible. Transfer the souffle to the prepared baking dish and bake until the top just feels set when you touch it in the center, about 25 minutes. Most souffle aficionados like theirs on the less-cooked side. Avoid opening the oven while the souffle is baking, so begin checking it closer to when it should be done.

Serve portions of the souffle on plates, making sure everyone gets some of the nice crust along with the moist interior, with a scoop of vanilla or coffee ice cream, or very cold creme anglaise. Although chocolate souffle is traditionally served hot from the oven, after it cools for 10 minutes it settles into a moist, warm mousse-like dessert. It’s also not bad the next day, at room temperature — for breakfast.