Preheat your oven to 350°F (175°C). Grease a 9x9-inch baking pan or line it with parchment paper.

In a medium saucepan, melt the butter over low heat. Remove from heat and stir in the sugar until well combined.

Beat in the eggs one at a time, mixing well after each addition, then stir in the vanilla extract.

In a separate bowl, whisk together the cocoa powder, flour, salt, and baking powder. Gradually add this dry mixture to the wet ingredients, stirring until just combined.

Fold in the Nutella until it is evenly incorporated into the batter.

Pour the batter into your prepared pan, spreading it evenly. Bake for 20 to 25 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.

Allow the brownies to cool in the pan for about 10 minutes before transferring to a wire rack. Once completely cool, slice and serve.