Preheat oven to 375F. Generously grease your ramekins with butter. You will need 4 10cm (4 inch) ramekins. In each one, add a tablespoon of sugar and tilt ramekin to ensure the sugar sticks to the sides and bottom.
In a saucepan, add 2 tablespoons of sugar, flour, salt and milk. Whisk to combine. Add the butter and heat over medium-high heat until the butter melts and the ingredients begin to simmer. Do not cook more than 30 seconds. Remove from heat and add the chopped chocolate. Whisk together to incorporate as it melts. Add the egg yolks and whisk to combine everything together. Set aside to cool.
In a separate bowl, begin to beat egg whites with a hand mixer until they become frothy. Add 4 teaspoons sugar and continue to beat until it forms stiff peaks.
Gradually fold the frothy egg whites into the chocolate batter using a spatula, adding the egg whites 1/3 at a time. Be careful not to vigorously mix and deflate the egg whites.
Carefully fill the ramekins 3/4 full. Place them on a baking sheet and bake in the oven for 17 minutes. This will produce a souffle with a soft, gooey center. For a well-baked souffle, cook for 20 minutes. Serve immediately as the souffle will deflate while it sits. If you wish, dust the souffles with cocoa powder or powdered sugar.