Preheat oven to 200°. Line 3 baking sheets with parchment paper. Draw 1 (10-inch) circle in center of each piece of parchment; set aside.
In the top of a double boiler, whisk together sugar and egg whites; place over simmering water. Cook sugar mixture until a candy thermometer registers 140˚. Remove from heat. Immediately pour mixture into the bowl of a stand mixer fitted with the whisk attachment. Beat on high speed for 10 minutes. Gently fold in cocoa.
Spread mixture onto drawn circles on parchment in prepared pans. Bake for 1 hour and 30 minutes. Turn oven off, and let meringues cool in oven with door closed for 8 hours.
In a medium bowl, beat mascarpone cheese and coffee with a mixer at medium speed until creamy. Stir in whipped topping and hazelnuts.
Place 1 meringue round on a serving plate. Spread with one-third of mascarpone mixture. Repeat layers with remaining meringues and remaining mascarpone mixture. Just before serving, drizzle with Chocolate Sauce. Garnish with hazelnuts and chocolate, if desired.
Chocolate Sauce
In a medium saucepan, combine butter and chocolate. Cook over medium heat, stirring frequently, until chocolate melts and mixture is smooth. Stir in sugars.
Add cream; bring to a boil over medium-high heat. Reduce heat, and simmer for 5 minutes, stirring frequently. Remove from heat, and stir in vanilla. Let cool completely.
Store covered in refrigerator for up to 1 week.
Recipe by Southern Lady Magazine at https://southernladymagazine.com/coffee-and-hazelnut-pavlova-recipe/