Preheat oven to 425°F (220°C). Brush four 6-ounce ramekins with melted butter, then dust generously with cocoa powder or sugar, tapping out excess. Place ramekins on a baking sheet.

In a microwave-safe bowl, combine chopped chocolate and butter. Microwave in 20-second bursts, stirring between each, until fully melted and smooth. Alternatively, use a double boiler. Let cool slightly.

In a large bowl, whisk together eggs, egg yolks, and sugar vigorously until thick and pale, about 2-3 minutes. You can use a hand mixer for speed. The mixture should fall in ribbons when lifted.

Pour the melted chocolate mixture into the egg mixture and fold gently with a spatula until just combined. Sift in the flour and salt, then fold again until no streaks remain. Do not overmix.

Spoon batter evenly into prepared ramekins, filling about 3/4 full. Bake for 12-14 minutes, until edges are set and the center is jiggly but reaches an internal temperature of 160°F (71°C) to ensure eggs are safely cooked. Do not overbake.

Remove from oven and let cool in ramekins for 1 minute. Run a knife around the edge to loosen. Invert each onto a serving plate, let sit a few seconds, then gently lift the ramekin. Dust with powdered sugar and serve immediately with ice cream or berries.