01 - Preheat the oven to 425°F. Grease four 6-oz ramekins with butter and lightly dust with flour or cocoa powder, tapping out excess.
02 - Melt the chocolate and butter together using a double boiler or microwave in short bursts, stirring until smooth. Let 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, placing 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 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 1 minute longer.
09 - Remove coulis from heat, strain through a fine sieve to remove seeds, and let cool.
10 - Let cakes rest 1 minute, run a knife around edges, and invert onto plates. Dust with icing sugar and serve immediately with raspberry coulis and fresh raspberries if desired.