Line 2 cookie sheets with parchment paper or Silpat mats.
In a bowl, combine the dry ingredients: flour, baking powder, and salt. Set aside.
In another bowl, using a hand mixer beat the butter with the sugar until smooth and creamy (2-3 minutes). Add in the egg, egg yolk, and vanilla extract, and mix again until smooth.
Add in the dry ingredients and mix until just combined, then gently fold in the chocolate chips.
Scoop out the cookie dough into 24 even balls, and place onto one baking sheet.
Flatten the balls slightly with your fingers, then place an oreo over half of the dough pieces, and cover with the other pieces. Very carefully roll each sandwich into a smooth cookie dough ball with the Oreo in the center.
Place the tray in the fridge for 30 minutes while you preheat the oven to 350°F/180°C.
Make sure that the cookies are placed about 2 inches apart on the baking sheet (you'll likely need to use two trays), then bake for 14-16 minutes or until the edges start turning golden brown. Remove from the oven, and allow to cool on the cookie sheet for 10 minutes then transfer to a wire rack to cool completely.
Notes
The chilling step is important, as it keeps your stuffed cookies from trying to spread too much in the oven.
Let the cookies cool before tasting them. The filling will be hot when these are fresh from the oven.
To Store: Keep these cookies in an airtight container in the fridge for up to 4 days, or freeze for up to two months.