Preheat oven to 350°F (175°C) and line an 8×8 inch baking pan with parchment paper.
In a bowl whisk melted butter and sugar until smooth.
Add eggs and vanilla extract and mix well.
Stir in cocoa powder, flour, salt, and baking powder until a thick batter forms.
Spread the brownie batter evenly into the prepared baking pan.
Drop spoonfuls of Nutella over the batter.
Use a knife or toothpick to swirl the Nutella gently through the batter.
Bake for 22–25 minutes until the center is set but still fudgy.
Let brownies cool before cutting into squares.
