Preheat oven to 350 degrees. Grease a 9x13 inch baking pan.

Cream the sugar and butter together with an electric mixer until light and fluffy.

Add the eggs, one at a time, mixing well after each addition. Scrape down sides as needed. Stir in milk and vanilla.

In a medium bowl, combine salt, baking soda, flour, and oats. Gradually add the dry mixture to the wet mixture and stir to combine. Press two-thirds of the cookie dough into the prepared pan.

Transfer the Dulce de Leche to a medium, microwave-safe bowl and microwave on high for about 60 seconds, stirring once halfway through.

Spread the Dulce de Leche over the cookie dough in the pan. Top with spoonfuls of the remaining cookie dough. Sprinkle with chocolate chips.

Bake for 25-30 minutes, or until golden brown. Cool completely on a wire rack before cutting into bars and serving.