01 - Preheat oven to 425°F. Generously butter four 6-ounce ramekins and lightly dust with cocoa powder, tapping out the excess.
02 - Melt chocolate and butter together in a heatproof bowl set over a pan of simmering water using a double boiler method. Stir until smooth, then remove from heat and let cool slightly.
03 - In a mixing bowl, whisk together eggs, egg yolks, and granulated sugar until pale and thick, approximately 2 minutes.
04 - Stir in the melted chocolate mixture and vanilla extract until combined.
05 - Sift in flour and salt and gently fold until just incorporated.
06 - Divide batter evenly among prepared ramekins. Place ramekins on a baking sheet.
07 - Bake for 12 minutes, or until the edges are set but centers remain soft.
08 - In a small saucepan, combine raspberries, sugar, and lemon juice. Cook over medium heat for 4 to 5 minutes, stirring and gently mashing until berries break down and sauce thickens slightly. Strain through a fine mesh sieve to remove seeds, if desired.
09 - Remove cakes from oven and let rest for 1 minute. Run a thin knife around the edges, then invert each cake onto a dessert plate.
10 - Drizzle with raspberry sauce, dust with powdered sugar, and serve immediately with fresh raspberries and ice cream or whipped cream, if desired.