Preheat the oven to 350°F (175°C). Grease a 9-inch pie dish lightly.
In a mixing bowl, whisk together the all-purpose flour, cocoa powder, baking soda, and salt. Set aside.
In a separate bowl, cream the softened butter and brown sugar together until light and fluffy.
Add the egg and vanilla extract to the butter mixture, beating until well combined.
Gradually add the dry ingredients to the wet ingredients, mixing until a dough forms.
Press the cookie dough evenly into the bottom and up the sides of the prepared pie dish.
Bake the crust in the preheated oven for 15 minutes, then remove and let cool slightly.
In a microwave-safe bowl, combine the Nutella and heavy cream. Heat in 15-second intervals, stirring until smooth and well combined.
Pour the Nutella mixture into the pre-baked cookie crust and spread evenly.
Return the pie to the oven for an additional 10 minutes to set, then remove and let cool at room temperature.
Once cooled, sprinkle a pinch of sea salt over the top for an extra flavor boost.
Slice and serve.