Preheat your oven to 200°C (392°F).
Grease and dust four 200ml (or larger) ramekins with butter and cocoa powder. This will help the cakes release easily after baking.
In a microwave-safe bowl, melt the dark chocolate and butter together. You can do this in the microwave in short 20-30 second bursts, stirring between each burst until the chocolate and butter are fully melted and combined. Alternatively, you can melt them together over a double boiler on the stove. Set this mixture aside to cool slightly.
In a separate bowl, whisk the eggs, granulated sugar, and vanilla extract together until the mixture becomes light and frothy.
Gradually pour the melted chocolate mixture into the egg mixture while whisking continuously. Make sure the chocolate mixture is not too hot to prevent cooking the eggs.
Sift the all-purpose flour into the chocolate mixture and add a pinch of salt. Gently fold the flour and salt into the mixture until just combined. Be careful not to overmix; you want a smooth batter.
Pour the batter evenly into the prepared ramekins, filling them about 2/3 full.
Place the ramekins on a baking sheet and then into the preheated oven.
Bake for about 12 minutes, or until the edges of the cakes are set but the centers are still slightly jiggly.
Remove the cakes from the oven and let them cool for 1-2 minutes.
To serve, run a knife around the edge of each ramekin to loosen the cake, then invert it onto a serving plate. The lava cake should easily come out with a gooey, molten center.
Dust with powdered sugar, add a scoop of ice cream or a dollop of whipped cream if desired, and serve immediately.Enjoy your delicious homemade chocolate lava cakes!