Milk and Cookie Bars

Cookie Bars:

• 1/2 cup unsalted butter
• 3/4 cup brown sugar
• 1/4 cup sugar
• 1 large egg
• 1 tsp vanilla extract
• 1 1/2 cups all-purpose flour
• 1/2 tsp baking powder
• 1/2 tsp baking soda
• 1/2 cup mini-chocolate chips

Milk Buttercream:

• 1 cup unsalted butter
• 3 cups icing (confectioners) sugar
• 1/3 cup whole milk
• 1 tsp vanilla extract preferably clear