HOW TO MAKE IT :
- Preheat oven to 350°F (175 degrees C). Prepare a 9×13-inch baking pan with baking spray, parchment, or the butter/flour method.
- In the bowl of a stand mixer (can also use hand-held mixer) beat the butter, brown sugar, and white sugar until well mixed, about 3 minutes.
- Add in eggs one at a time, mixing well after each addition.
- With mixer on low, add in the vanilla extract.
- Remove bowl from stand mixer and add in salt, baking soda, baking powder, flour, rolled oats, plus semi-sweet chocolate chips.
- Stir by hand to moisten all ingredients.
- Spread 1/2 mixture into the prepared baking pan. Pour milk chocolate chips on top of mixture. Carefully press remaining cookie mixture on top of chocolate.
- Bake in the preheated oven until golden brown, 24 to 30 minutes.
- Let cool in the pan for about 5 minutes before cutting into bars.