Step 1: Preheat your oven to 425°F (218°C). Grease two 6-ounce ramekins with butter and dust with cocoa powder, tapping out the excess.
Step 2: In a medium microwave-safe bowl, combine the chopped chocolate and butter. Microwave in 30-second intervals, stirring between each, until completely smooth and melted.
Step 3: In a separate bowl, whisk together the eggs, egg yolks, sugar, and salt for about 2 minutes until the mixture is thick and light in color.
Step 4: Slowly pour the melted chocolate into the egg mixture while whisking constantly to ensure the eggs do not scramble.
Step 5: Sift the flour over the batter and gently fold it in with a spatula until just combined.
Step 6: Divide the batter evenly between the prepared ramekins.
Step 7: Bake for 12-14 minutes. The sides should be set, but the center should still be slightly soft to the touch.
Step 8: Let the cakes cool in the ramekins for 1 minute, then carefully run a knife around the edges and invert onto dessert plates.