Preheat the oven to 350°F. Line a 9×13-inch baking dish with parchment paper, leaving some overhang for easy removal of the brownies.

In a large bowl whisk flour, cornstarch, cocoa, baking powder, and salt. Set aside.

To the bowl of a stand mixer fitted with the paddle attachment, add the eggs, sugar, butter, and vanilla. Beat on medium speed until light and fluffy.

With the mixer off, add the flour mixture. Turn the mixer on low and mix until the ingredients are well combined.

Pour brownies into the prepared baking dish and bake for 30-35 minutes, or until done. Fudgy brownies are done baking when the edges appear set, but the center is still shiny, or moist.

Let the brownies cool at room temperature.

In a microwave-safe bowl, heat ½ cup of the heavy cream for 50 seconds.

Add the chocolate chips to the cream and stir until the chocolate has melted. Set aside to cool.

Pour the remaining 1 cup of heavy cream into a medium bowl. Using a hand-held or stand mixer, beat until soft peaks form. Continue whipping the cream until stiff peaks form.

Fold the cooled chocolate mixture into the whipped cream until combined.

Pour the mousse over the cooled brownies and spread it into an even layer. Garnish with chocolate curls (optional).

Refrigerate 2 hours (up to overnight) before serving.