Preheat oven to 350 degrees.
Line a 9-inch cast iron skillet with parchment paper and set aside.
In a large bowl, combine the butter, sugar and vanilla and whisk until light and creamy.
Add egg and whisk until combined.
Add flour, baking soda and salt and mix just until combined.
Fold in half of the chocolate chips and spoon half of the batter into the skillet.
Melt the Nutella in the microwave for 30 seconds until it becomes thinner and pour over cookie dough. Spread within 1-inch of edges.
Top with the remaining cookie batter, spreading to cover the Nutella layer. Sprinkle with remaining chocolate chips.
Bake for 25-30 minutes for a soft cookie or cover with foil and bake for 10 more minutes for a more set cookie.
Cool about 10 minutes, cut into wedges and serve. Great with vanilla ice cream.