01 - Preheat oven to 400°F. Generously butter four 6-ounce ramekins and dust with granulated sugar; tap out excess.
02 - In a heatproof bowl set over simmering water, melt chocolate with 2 tablespoons butter, stirring until smooth. Remove from heat and cool slightly.
03 - In a large bowl, whisk together egg yolks and half the sugar until pale and thick. Stir in vanilla and salt. Add melted chocolate mixture and flour; mix until combined.
04 - In a clean bowl, beat egg whites until soft peaks form. Gradually add remaining sugar and beat until glossy, stiff peaks form.
05 - Gently fold one-third of the egg whites into the chocolate mixture to lighten. Carefully fold in the remaining egg whites until just incorporated, taking care not to deflate the mixture.
06 - Divide the batter evenly among prepared ramekins. Run your thumb around the inside edge of each ramekin to help the soufflés rise evenly.
07 - Place ramekins on a baking sheet and bake for 14–18 minutes, until risen and barely set in the center.
08 - In a small saucepan, combine raspberries, sugar, lemon juice, and water (if using frozen berries). Cook over medium heat for 3–4 minutes, until raspberries break down. Strain through a fine mesh sieve to remove seeds. Serve warm or at room temperature.
09 - Dust soufflés with powdered sugar and serve immediately with raspberry sauce.