Preheat oven to 350°F. Grease or line a 9 x 9 baking pan with parchment paper. Cream butter and sugar until light and fluffy. Add in flour, vanilla and egg and mix on medium speed until smooth dough forms. Add in Oreos and mix on low speed until Oreos are crushed and evenly incorporated into the dough.
Scoop dough into 9 x 9 baking pan and try your best to spread evenly across the entire pan. Dough will be very sticky. Don't worry if you can't smooth out top because once it begins to cook in the oven, it will smooth out.
Bake 25-30 minutes until blondies begin to turn a light brown and toothpick inserted comes out clean. Let blondies cool completely in the pan (at least 1 hour or longer) before cutting and serving. Letting them cool will allow them to settle and become dense and chewy.
The nutrition information provided are only estimates based on an online nutritional calculator. This is not a comprehensive list of all the nutrients in the recipe (i.e., does not include vitamins, cholesterol, etc). I am not a certified nutritionist. Please consult a nutritionist or doctor for accurate information and any dietary restrictions and concerns you may have.