Preheat oven to 350°F (175°C). Grease and line an 8×8-inch baking pan with parchment paper.

In a large mixing bowl, combine melted butter, sugar, and vanilla extract. Whisk until smooth.

Add eggs one at a time, whisking after each addition.

Stir in Nutella until fully incorporated.

In a separate bowl, whisk together flour, salt, and baking powder. Gradually fold into the wet mixture.

Pour batter into prepared pan, smoothing the top.

Bake for 20–25 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.

Allow to cool completely in the pan before slicing into squares.