Step 1

Preheat the oven to 350 degrees F. Line an 8-by-8-inch square baking pan with parchment, leaving a 2-inch overhang on 2 opposite sides.

Step 2

Place 1 1/3 cups of the chocolate chips in a medium microwave-safe bowl. Microwave the chocolate until melted, stirring halfway through, about 2 minutes. Let cool slightly, about 5 minutes.

Step 3

Separate the egg whites into a large bowl. Add the yolks and 2 tablespoons water to the chocolate, then whisk until smooth and combined; set aside, Whip the egg whites with an electric mixer on medium-high speed until stiff peaks form. Gently fold 1/3 of the chocolate mixture into the egg whites, mixing until just combined (you want the whites to stay as fluffy as possible). Repeat 2 more times with the remaining chocolate, folding until well combined.

Step 4

Pour the batter into the prepared pan and bake until the brownies are set and a toothpick inserted into the center comes out clean, 25 to 27 minutes. Sprinkle the remaining 1/3 cup chocolate chips over the top and return to the oven; bake until just beginning to melt, about 2 minutes. Remove from oven and spread the melted chocolate all over the top of the brownies with an offset spatula.

Step 5

Let cool completely in the pan, about 30 minutes, Use the parchment overhang to remove the brownies from the pan and cut into squares.