Preheat the oven to 350°F. Grease a 9x9 square baking pan.
In a small saucepan, melt the butter over low heat. Remove the saucepan from the heat, and stir in the chocolate chips, vanilla, and salt until the chocolate has melted.
Using a stand mixer or a hand mixer, add the sugar and egg whites into a large bowl and beat on medium speed for 5 minutes. Mixture should be somewhat thick and foamy.
Add the butter and chocolate mixture to the egg mixture and mix until it becomes incorporated. Slowly mix in the flour until it is well combined.
Spread the batter into the prepared pan. Bake for 30-35 minutes until the center is no longer jiggly and a toothpick inserted into the center of the brownies contains moist crumbs.
Allow brownies to cool, then cut into squares and serve.