Preheat oven to 425 degrees and place rack in center of oven. Spray ramekins thoroughly with cooking spray and place on baking sheet.
Place butter in microwave-safe bowl and melt completely. Add chopped chocolate, stir until combined. Set aside and allow chocolate to cool slightly.
In a separate bowl, beat eggs, sugar and salt with hand mixer until thickened, pale and tripled in volume (about 4-5 minutes). Fold chocolate into egg mixture until completely incorporated. Gently fold in flour.
Spoon batter into prepared ramekins and bake 9-12 minutes until firm along edges, but soft in center. Allow to cool 1 minute before unmolding.
Simply run knife along sides of ramekin to loosen edges and place dessert plate upside down on top of ramekins and invert then carefully unmold cakes.
Garnish as desired and serve immediately.
Notes
Want to make the lava cake in advance? Just pour completed batter into ramekins, cover and refrigerate. Return to room temperature before baking!