Preheat oven to 425 F. Spray inside of four ramekins with non stick spray. Melt chocolate chips with butter in the microwave in 30 second increments stirring in between until smooth.
In a large mixing bowl, whisk together the sugar, eggs, egg yolks, and vanilla extract until light and frothy. Slowly stir in the melted chocolate mixture until well combined.
Add the flour and salt and whisk until just combined. Divide the batter evenly between the four ramekins. Bake for 12-15 minutes, until the edges are firm but the centers are still a bit jiggly.
Let the cakes cool for 1-2 minutes, then run a knife around the edges of the ramekins to loosen the cakes.