Chocolate & Hazelnut Meringue Cake

INGREDIENTS

• For the cake:
• 10 tablespoons unsalted butter, plus more for pan
• 3/4 cup firmly packed light-brown sugar
• 6 large whole eggs, separated
• 12 ounces bittersweet chocolate, melted and cooled
• 1 1/2 tablespoons espresso
• 1 1/2 tablespoons rum
• 1/4 teaspoon salt
• For the meringue:
• 4 ounces bittersweet chocolate, roughly chopped (1 cup)
• 1 cup hazelnuts (about 4 ounces), toasted, skinned, and roughly chopped
• 1 tablespoon cornstarch
• 4 large egg whites
• 3/4 cup sugar