Preheat the oven to 350°F (175°C). Grease a 9x13 inch baking pan.

In a mixing bowl, cream together the softened butter, brown sugar, and granulated sugar until smooth.

Beat in the eggs one at a time, then stir in the vanilla extract.

In another bowl, combine the flour, baking soda, and salt. Gradually add to the creamed mixture.

Stir in the oats until evenly mixed.

Spread the mixture evenly into the prepared baking pan.

Bake for 20-25 minutes or until the edges are golden brown. Let cool completely.

In a small bowl, whisk together the powdered sugar, milk, and vanilla extract until smooth.

Spread the icing over the cooled cookie bars.

Allow the icing to set before cutting into bars.