01 - Preheat oven to 400°F (200°C). Generously butter four 6-ounce ramekins and dust with granulated sugar, tapping out any excess.
02 - In a heatproof bowl positioned over simmering water, melt the chocolate and 2 tablespoons of butter, stirring until completely smooth. Remove from heat and allow to cool slightly.
03 - In a large mixing bowl, whisk together the egg yolks and 2 tablespoons of granulated sugar until the mixture is pale and thick. Incorporate the vanilla extract and salt. Gently fold in the melted chocolate mixture and flour until just combined.
04 - In a separate, clean bowl, beat the egg whites until soft peaks begin to form. Gradually add the remaining 2 tablespoons of sugar and continue beating until glossy, stiff peaks are achieved.
05 - Gently fold one-third of the beaten egg whites into the chocolate mixture to lighten its consistency. Carefully incorporate the remaining egg whites until just combined, taking care not to deflate the delicate foam.
06 - Evenly distribute the soufflé batter among the prepared ramekins. For an even rise, run your thumb around the inside edge of each ramekin to create a slight separation.
07 - Arrange the ramekins on a baking sheet and bake for 14–18 minutes, or until the soufflés are beautifully risen and just barely set in the center.
08 - While the soufflés are baking, prepare the raspberry sauce. In a small saucepan, combine the raspberries, granulated sugar, lemon juice, and water (if using frozen berries). Cook over medium heat for 3–4 minutes, until the raspberries have softened and broken down. Strain the mixture through a fine mesh sieve to remove any seeds, yielding a smooth sauce. Serve warm or at room temperature.
09 - Lightly dust the baked soufflés with powdered sugar and serve immediately with the prepared raspberry sauce.