Step 1: Preheat the Oven

1. Preheat your oven to 425°F (220°C).
2. Grease four 6-ounce ramekins with butter and lightly dust with flour or cocoa powder.

Step 2: Melt Chocolate and Butter

1. In a microwave-safe bowl, combine the unsalted butter and chocolate chips. Microwave in 30-second intervals, stirring in between, until completely melted and smooth. Let it cool slightly.

Step 3: Mix the Batter

1. In a separate bowl, whisk together the eggs, egg yolks, and granulated sugar until well combined and slightly frothy.
2. Gradually pour the melted chocolate mixture into the egg mixture, whisking continuously to prevent the eggs from cooking.
3. Gently fold in the flour, salt, and vanilla extract until just combined. Be careful not to overmix.

Step 4: Fill Ramekins

1. Divide the batter evenly among the prepared ramekins, filling each about 3/4 full.

Step 5: Bake the Cakes

1. Place the ramekins on a baking sheet and bake in the preheated oven for 12-14 minutes. The edges should be firm, but the center should still be soft and slightly jiggly.

Step 6: Serve

1. Remove the ramekins from the oven and let them cool for about 1 minute.
2. Carefully run a knife around the edges of each ramekin to loosen the cakes. Invert the ramekins onto individual plates and gently lift them off.
3. Dust with powdered sugar and serve immediately, preferably with vanilla ice cream or whipped cream.