Step 1

A 9”-diameter springform pan

Step 2

Preheat oven to 350°. Lightly butter springform pan and dust with sugar, tapping out any excess.

Step 3

Combine chocolate, oil, and ½ cup butter in a large heatproof bowl. Set over a saucepan of simmering water and heat, stirring often, until melted. Remove bowl from saucepan.

Step 4

Separate 4 eggs, placing whites and yolks in separate medium bowls. Add cocoa powder, vanilla, salt, ¼ cup sugar, and remaining 2 eggs to bowl with yolks and whisk until mixture is smooth. Gradually whisk yolk mixture into chocolate mixture, blending well.

Step 5

Using an electric mixer on high speed, beat egg whites until frothy. With mixer running, gradually beat in ½ cup sugar; beat until firm peaks form.

Step 6

Gently fold egg whites into chocolate mixture in 2 additions, folding just until incorporated between additions. Scrape batter into prepared pan; smooth top and sprinkle with remaining 2 Tbsp. sugar.

Step 7

Bake until top is puffed and starting to crack and cake is pulling away from edge of pan, 35-45 minutes. Transfer to a wire rack and let cake cool completely in pan (cake will collapse in the center and crack further as it cools).

Step 8

DO AHEAD: Cake can be made 1 day ahead. Cover in pan and store airtight at room temperature.

Step 9

Using an electric mixer on medium-high speed, beat cream, mascarpone, and powdered sugar in a medium bowl until soft peaks form.

Step 10

Remove sides of springform pan from cake. Mound whipped cream mixture in center of cake.