Preheat oven to 350 degrees Fahrenheit (180 degrees Celsius).

Line a 9×13-inch (23×33-centimeter) pan with baking paper.

In a small saucepan, melt the chocolate chips with oil, stirring occasionally. Allow to cool.

With a mixer, beat egg whites with 1/2 cup sugar until stiff.

In a separate bowl, beat egg yolks, remaining sugar, and vanilla extract until light and fluffy. Beat melted chocolate into yolk mixture.

Gently fold egg whites into yolk mixture.

Pour half of the batter into the prepared pan and bake for 30 minutes or until firm.

Refrigerate remaining batter.

When cake is cooled, spread refrigerated batter on top of cake and freeze, for at least three hours.

For the whipped topping, beat ingredients until stiff.

Spread whipped topping over frozen cake, cover tightly with aluminum foil, and return to the freezer until ready to serve.