01 - Preheat oven to 425°F. Grease four 6-oz ramekins with butter and dust lightly with flour or cocoa powder, tapping out the excess.
02 - Melt chocolate and butter together in a heatproof bowl over simmering water or microwave in short bursts. Stir until smooth and allow to cool slightly.
03 - In a medium bowl, whisk eggs, egg yolks, and sugar until pale and thick, about 2 minutes.
04 - Gently fold the melted chocolate mixture into the egg mixture until just combined.
05 - Sift in flour and salt, folding gently until the batter is smooth.
06 - Divide batter evenly among prepared ramekins and place them on a baking tray.
07 - Bake for 11 to 12 minutes until edges are set but centers remain soft. Avoid overbaking.
08 - While baking, combine raspberries, sugar, and lemon juice in a small saucepan. Cook over medium heat for 3 to 4 minutes until berries break down. For thicker coulis, stir in cornstarch dissolved in 1 tsp water and cook an additional minute.
09 - Remove from heat and strain through a fine sieve to remove seeds. Let cool.
10 - Let cakes rest for 1 minute after baking. Run a knife around edges and invert each cake onto serving plates. Dust with icing sugar and serve immediately with raspberry coulis and optional fresh raspberries.