Grease or spray a 9 x 13 inch pan. Melt the butter in a small saucepan. Cool. Whisk the cooled butter, brown sugar, eggs and vanilla in a large bowl until smooth.
Whisk the flour, baking soda and salt in another bowl. Stir the dry ingredients into the wet ingredients with a spoon, taking care not to over mix. The batter should be thick and all of the flour mixture should be fully incorporated. Fold in the chocolate chips.
Spread the batter evenly in the prepared pan. Bake until the edges are browned and the center is completely set, about 25 minutes. Cool completely. Cut into 24 pieces and serve.