Step 1

Finely chop the peanut brittle using a sharp knife, serrated if you like. The pieces of brittle should be roughly the size of grains of rice.

Step 2

In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter, sugar, and corn syrup on medium high for 3 minutes. Scrape down the bowl. Add the peanut butter and mix to combine. Add the eggs and vanilla and mix on medium-high for 30 seconds. Scrape down the bowl again, before continuing to mix on medium-high for 3 minutes.

Step 3

With the mixer on low, add the flour, baking powder, baking soda, and salt. Mix until just combined, less than 1 minute. Scrape down the bowl. Continuing on low, add the peanut brittle and mix no longer than 30 seconds. Remove the bowl from the mixer and briefly mix by hand to make sure there are no ingredients lingering at the bottom of the bowl.

Step 4

Using a regular sized ice cream scoop, scoop the dough onto a parchment lined baking sheet. Flatten the tops of the cookies with your hand, but keep the cookies themselves tall. Wrap the pan tightly with plastic wrap and place in the refrigerator for at least 2 hours and up to 1 week.

Step 5

After the cookies have been chilled, preheat oven to 350 degrees F. Place the cookies on parchment lined baking sheets, 5 per sheet, spaced as far apart as possible. Place any cookies not being baked at the time back in the refrigerator. Bake for 15-18 minutes, rotating halfway through if necessary, until the cookies have puffed, cracked, and spread, but are still incredibly soft to the touch. Be sure to follow all directions exactly or these cookies will not turn out properly.

Step 6

Allow cookies to cool complete on pans. They may be stored at room temperature in an airtight container for up to 5 days, or frozen, wrapped in parchment and foil and placed in a zipper bag for up to 3 months. Thaw at room temperature for about 1 hour.