01 - Preheat oven to 425°F. Grease four 6-oz ramekins with butter and lightly dust with flour or cocoa powder; tap out excess.
02 - Combine chocolate and butter in a heatproof bowl over simmering water or in short microwave bursts. Stir until smooth and allow to cool slightly.
03 - In a medium bowl, whisk eggs, egg yolks, and sugar until pale and thick, approximately 2 minutes.
04 - Gently fold the melted chocolate mixture into the egg mixture until just incorporated.
05 - Sift flour and salt into the batter and fold gently until smooth.
06 - Divide the 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 - In a small saucepan, combine raspberries, sugar, and lemon juice. Cook over medium heat for 3 to 4 minutes until berries break down. For thicker coulis, stir in cornstarch dissolved in 1 teaspoon water and cook 1 minute longer.
09 - Remove from heat and strain through a fine sieve to remove seeds. Allow to cool.
10 - Let cakes rest 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 fresh raspberries if desired.