Fallen Chocolate Cake

INGREDIENTS

• 1/2 (1 stick) unsalted butter, cut into 1-inch pieces, plus more, room temperature, for pan
• 3/4 plus 2 tablespoons sugar, divided, plus more for pan
• 10 semisweet or bittersweet chocolate (61%-72% cacao), coarsely chopped
• 2 vegetable oil
• 6 large eggs
• 2 natural unsweetened cocoa powder
• 1 vanilla extract
• 3/4 kosher salt
• 1 chilled heavy cream
• 1/2 mascarpone
• 3 powdered sugar
• A 9-inch-diameter springform pan