Salted Caramel "Ding Dong" Cake

INGREDIENTS

• 2 cups sugar
• 1 1/8 teaspoons kosher salt
• 1 teaspoon kosher salt
• 1 1/4 teaspoons unflavored gelatin
• 1 cup natural unsweetened cocoa powder
• 3/4 cup buttermilk
• 1 cup sugar
• 4 ounces semisweet or bittersweet chocolate, chopped
• 1 1/2 cups chilled heavy cream
• 9 ounces semisweet or bittersweet chocolate, chopped
• 1/2 cup powdered sugar
• 1 1/2 cups heavy cream
• Flaky sea salt (such as Maldon)
• 1 1/2 teaspoons vanilla extract
• 1 teaspoon baking soda
• 3 large eggs
• Nonstick vegetable oil spray
• 2 cups cake flour
• 1 cup hot strong coffee
• 1 teaspoon vanilla extract
• 1 cup (2 sticks) unsalted butter, room temperature
• 1 teaspoon baking powder
• 1 vanilla bean, split lengthwise