Salted Caramel Ding Dong Cake

Name: Salted Caramel Ding Dong Cake
Ingredients: Nonstick vegetable oil spray; 1 cup natural unsweetened cocoa powder; 4 ounces semisweet or bittersweet chocolate, chopped; 1 cup hot strong coffee; 3 /4 cup buttermilk; 1 1/2 teaspoons vanilla extract; 2 cups cake flour; 1 teaspoon baking powder; 1 teaspoon baking soda; 1 teaspoon kosher salt; 2 cups sugar; 1 cup (2 sticks) unsalted butter, room temperature; 3 large eggs; 9 ounces semisweet or bittersweet chocolate, chopped; 1 1/8 teaspoons kosher salt; 1 cup sugar; 1 1/2 cups heavy cream; 1 teaspoon vanilla extract; 1 1/4 teaspoons unflavored gelatin; 1 1/2 cups chilled heavy cream; 1 /2 cup powdered sugar; 1 vanilla bean, split lengthwise; Flaky sea salt (such as Maldon); Two 9-inch-diameter cake pans with 2-inch-high sides; a 9-inch-diameter springform pan