1 cup (170 grams) semisweet chocolate chips
1 1/2 sticks (170 grams) unsalted butter, cut into pieces
1/2 cup dark chocolate, chopped
1 1/4 cups (245 grams) granulated sugar
1/2 cup (150 grams) Nutella
3 large eggs plus 1 egg yolk
1 teaspoon vanilla extract
3/4 cup (96 grams) all-purpose flour
1/4 cup unsweetened (25 grams) cocoa powder
1/4 teaspoon fine sea salt
1 tsp baking powder
1/2 cup chocolate chips for topping the batter if desired
Preheat the oven to 350°F. Line an 8x8-inch *metal* baking pan with foil or parchment, leaving an overhang, and spray with nonstick cooking spray.
In a large pan melt the butter on the stove then add the chocolate chips and dark chocolate and let sit for 4 minutes unit melted. Stir in the Nutella.
In a large bowl, use an electric mixer to beat the eggs and sugar on medium-high speed until light and thick, about 3 minutes. Beat in the vanilla extract. Stir in the cooled chocolate mixture with a rubber spatula and add the cocoa. Add the flour, baking powderand salt, folding gently until combined.
Pour the batter into the prepared baking pan, add some chocolate chips on top . Bake until a tester comes out with moist crumbs still attached, 35 to 40. Do not overbake, you want to error on the side of underbaking. Let cool to room temperature. Serve at room temperature, warmed, or chilled