Preheat the oven to 375°F (190°C). Make sure the racks are not too close together so the souffle can rise up while baking.

Generously butter the inside of 4 ramekins and coat bottom and sides with sugar. Tap out excess sugar. This step is super important as this means the souffle will glide up with ease during baking.

Place the flour, 2 tablespoons of sugar and salt in a medium saucepan. Whisk in the milk until smooth and there are no lumps.

Over medium heat, add the butter and bring to a gentle simmer, whisking until the mixture has thickened about 2 to 3 minutes.

Remove from the heat and stir (with a spatula) in the chocolate until smooth. Allow cooling slightly.

Stir in yolks and vanilla. Set aside to cool down. (Note: At this point, the base can be refrigerated for 3 days. Bring to room temperature before folding in the whites).

Using a stand mixer fitted with the whisk attachment, or a handheld electric mixer, whip the egg whites and cream of tartar on low speed for 2 minutes, or until bubbles start to form.

Turn up the speed to high, and with the mixer running slowly add the remaining 2 tablespoons of sugar, 1 tablespoon at a time until it is all incorporated. The egg whites will double in volume and become shiny.

Fold one-third of the egg whites into the chocolate mixture until fully incorporated. Gradually fold in remaining egg whites one-third at a time until no streaks of egg whites remain. Mixture should be light and smooth.

Pour the batter into the prepared ramekins to the top and smooth the top evenly with a spatula if needed.

Bake for 16 to 18 minutes until puffed and set. Here's the hard part, this is all about TIMING! First let it bake, undisturbed for at least 80 percent of its cooking time. Then, for the remainder of the cooking time, watch for the crown of the souffle to become nicely browned. It should not wobble too much once ready. Say a prayer and remove it.

Dust with powdered sugar and serve IMMEDIATELY.