Preheat the oven to 425°F 218°C and grease four ramekins with butter then dust with cocoa powder
Melt the dark chocolate and butter together using a double boiler or in the microwave in 30-second intervals stirring in between until smooth
In a separate bowl whisk the eggs egg yolks sugar and vanilla extract until the mixture becomes light and fluffy
Slowly pour the melted chocolate mixture into the egg mixture stirring continuously to prevent the eggs from scrambling
Gently fold in the flour and salt until just combined being careful not to overmix
Divide the batter evenly between the prepared ramekins filling them about three-quarters full
Bake in the preheated oven for 10 to 12 minutes until the edges are set but the center remains soft and slightly jiggly
Remove from the oven and let the cakes rest for 1 minute before running a knife around the edges to loosen them
Carefully invert each ramekin onto a plate tap gently and lift to reveal the lava cake
Serve immediately with vanilla ice cream fresh berries or a dusting of powdered sugar