Preheat your oven to 425°F (220°C). Grease four ramekins with butter and lightly dust with flour, tapping out the excess.
In a microwave-safe bowl, combine the chopped dark chocolate and unsalted butter. Microwave in 30-second intervals, stirring in between until completely melted and smooth. Let it cool slightly.
In a separate bowl, whisk together the eggs, egg yolks, granulated sugar, and vanilla extract until pale and thickened.
Pour the melted chocolate mixture into the egg mixture and stir until combined.
Gently fold in the flour and salt until just incorporated. Be careful not to overmix.
Spoon half of the chocolate batter into each prepared ramekin. Place 3-4 fresh raspberries in the center of each ramekin, then top with the remaining chocolate batter, dividing it evenly.
Place the ramekins on a baking tray and bake for 12-14 minutes, or until the edges look set but the center is still soft.
Once baked, remove from the oven and let them rest for 1 minute. Carefully invert each ramekin onto a plate and gently tap to release the lava cake.
Dust with powdered sugar and garnish with extra raspberries on top for a fresh touch.