Preheat the oven to 325 degrees Fahrenheit. Grease a 10-inch skillet, and set aside.
In the bowl of a stand mixer fitted with a paddle attachment, beat the eggs and sugar on medium-high speed for 5 minutes or until the mixture is thick and light yellow in color.
4 large eggs, 1 ½ cups granulated sugar
Add the cocoa powder, instant espresso, flour, and salt. Mix until just combined.
¾ cup unsweetened cocoa powder, 2 Tablespoons instant espresso powder, ⅓ cup all-purpose flour, ½ teaspoon kosher salt
Turn the mixer to low, and slowly pour in the melted, cooled butter, Nutella, and vanilla mixing until no streaks remain.
1 ¾ sticks, ⅓ cup Nutella spread, 2 teaspoons vanilla extract
Gently fold in the chocolate pieces.
4 ounces chocolate
Pour the batter into the skillet. Bake for 25 minutes or until the brownie is puffed on top but still wiggly in the center. Note: The longer the brownie bakes, the more set the center will be.
Remove the skillet from the oven, and let it cool slightly in the skillet.
Serve warm topped with a scoop of vanilla ice cream, if desired.
Optional: vanilla ice cream for topping