Preheat oven to 400 degrees Fahrenheit. Spray bottom and sides of ramekin well, and dust with cacao powder to coat.

Melt chocolate chips and oil in the microwave for one minute, stirring after 30 seconds, or over a double boiler, mixing until smooth.

In a separate bowl, beat eggs, sugar, vanilla and salt about two minutes, until light and fluffy. Mix in melted chocolate to combine, then add flour. Mix well.

Pour half into the ramekin, add a square of dark chocolate in the middle, then top with the remaining batter.

Bake for seven to eight minutes. The middle of the cake should look a bit soft and undercooked.

Let cool for a few minutes. Then run a knife around the sides to loosen the cake and invert onto a serving plate.

Top with dark chocolate shavings and enjoy!