Preheat oven to 325 degrees F. Coat an 8x8 pan with foil and nonstick spray for easy removal.
Melt 1 cup semisweet chocolate chips and 1/2 stick butter in a saucepan over low heat, stirring. Off the heat whisk in 1/4 cup brown sugar and 1/2 cup granulated sugar.
Transfer mixture to a medium bowl. Whisk in 2 eggs, one at a time, and 1/2 teaspoon of vanilla.
Stir in flour and salt.
Add batter to prepared baking pan and bake in preheated oven for 45 minutes, until toothpick comes out clean. Let cool completely before cutting into bars.