Melt the butter in a microwave safe bowl, then let it sit and cool for a few minutes. With a paper towel or pastry brush, spread some of the butter in a 9x13 pan, covering the bottom and sides.
Add the brown sugar, eggs, and vanilla into the melted butter and mix well.
Measure the flour (spoon the flour into your measuring cup, then level it with a knife) and mix it with the baking soda. Add the flour mixture into the butter mixture. Mix well.
Pour in the chocolate chips and stir to combine. Spread the batter as evenly as you can in the 9x13 pan.
Bake in a preheated 350 degree oven until the edges are browned, and the middle is set--around 35 to 40 minutes in my oven.
Let cool for about an hour before cutting into squares.
Notes
Love chocolate and peanut butter? Use 1 bag of chocolate chips and 1 bag of peanut butter chips, or leave out both bags and cover the top with mini Reese's PB Cups--pushing them into the batter.