Position a rack into the center of the oven, then preheat the oven to 350 degrees F.
Coat a 9-inch Savarin mold or a tube pan with cooking spray.
In a heatproof bowl, add the chocolate.
In a saucepan over medium heat, warm the heavy cream until small bubbles form around the edge of the pan.
Pour the heated cream over the chocolate and allow it to sit for 5 minutes.
Add the butter and 1 tablespoon of the confectioners' sugar to the chocolate and stir until smooth.
Set the chocolate mixture aside to cool.
Sift the flour, the cornstarch, the salt, and the cocoa powder through a fine strainer into a mixing bowl and set it aside.
In another large bowl, add the egg whites and whip until soft peaks form and set it aside.
In another mixing bowl, whisk the egg yolks, the granulated sugar, the yogurt, and the vanilla until smooth and airy.
Slowly add the oil to the egg yolk mixture and whisk continuously to incorporate.
Add the flour mixture to the egg yolk mixture and stir with a wooden spoon or spatula just until the flour is no longer visible.
Fold the whipped egg whites into the batter until just incorporated.
Evenly pour the batter into the prepared pan.
Bake the cake until the edges begin to pull away from the sides of the pan and a toothpick inserted into the middle comes out clean, about 30-35 minutes.
Let the cake cool in the pan for 10 minutes.
Gently invert the cake onto a wire rack to cool completely.
Place the cake, cracked-side up, onto a large plate or serving platter.
Pour the glaze over the top of the cake.
Fill the hole with the whipped cream and top with the sweetened berries.
Sprinkle the cake with the extra confectioners' sugar, then slice and serve.