1. Preheat the oven to 350 degrees. Line two half-sheet pans with parchment paper. Sift the flour, baking soda, baking powder, and salt, and set aside.
2. In the bowl of a stand mixer, beat the butter until creamy. Add the granulated sugar and brown sugar and mix until fluffy and pale. Beat in the peanut butter, and then add the eggs and vanilla. Mix in the flour mixture, along with the ground peanuts until well incorporated.
3. Using a tablespoon-sized scoop, drop the cookies onto the prepared pans and bake for 10 minutes. Cool completely with wire racks.
4. Place 1 teaspoon of Speculoos in the center of each cookie, and sandwich with another cookie.