In a small bowl, combine all the ingredients for the peanut butter filling. Mix well with a whisk. Cover and cool in the refrigerator.

In a large bowl, whisk together the flour, baking soda, and baking powder. Then add in the salt and oats. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl if using a handheld mixer, cream together the butter, peanut butter, white and brown sugars on medium speed until light and fluffy.

Turn the mixer down to low and add the eggs one at a time until each one is fully incorporated before adding the next. Add the vanilla and continue to mix.

Slowly add the dry ingredients in 3 or 4 additions and mix until just combined - do not over mix.

Use a cookie (or ice cream) scoop to portion out the dough onto a parchment or wax paper lined baking sheet. You may need two baking sheets. Place them close together and chill in the refrigerator for at least 2 hours.

After the cookie dough has thoroughly chilled, preheat your oven to 375 degrees F. Arrange only 8 cookies on a parchment-lined (or Silpat-lined, like I did) baking sheet. Stack this baking sheet inside another baking sheet so it's double-panned.

Bake the cookies for about 6 minutes, rotate the pan, and bake for an additional 6 minutes (12 minutes total) or until the cookies are golden. Bake the cookies in several batches.

Remove the cookies and allow them to cool completely on a wire rack before filing them.

To fill the cookies, turn a cookie over and spread about 2 teaspoons of the chilled peanut butter filling onto the flat side of the cookie. Top it with another cookie, flat side down, and press gently. Repeat with the remaining cookies and filling.