01 - Preheat the oven to 425°F. Grease four 6 oz ramekins with butter and dust with cocoa powder, tapping out the excess.
02 - Melt the chocolate and butter together in a heatproof bowl set over a pot of simmering water (double boiler), stirring until smooth. Remove from heat and let cool slightly.
03 - In a separate bowl, whisk together the sugar, eggs, and egg yolks until thick and pale.
04 - Stir the melted chocolate mixture into the egg mixture. Add vanilla extract and salt.
05 - Sift in the flour and gently fold until just combined; do not overmix.
06 - Divide the batter evenly among the prepared ramekins. Place ramekins on a baking sheet.
07 - Bake for 11-12 minutes, until the edges are set but the centers are still soft. Do not overbake.
08 - While the cakes bake, combine raspberries, sugar, lemon juice, and water in a small saucepan over medium heat. Cook for 5 minutes, stirring, until raspberries break down.
09 - Strain the coulis through a fine sieve into a bowl to remove seeds. Let cool.
10 - Remove cakes from the oven. Let them rest for 1 minute, then run a knife around the edges and invert onto serving plates. Dust with powdered sugar, drizzle with raspberry coulis, and garnish with fresh raspberries and mint if desired. Serve immediately.