Preheat oven to 350 degrees.

In the bowl for an electric mixer cream together the butter, shortening, sugar and brown sugar. Add in the eggs and vanilla, mix until well combined.

Stir in flour, salt and baking soda. Fold in the chocolate chips.

Scoop small balls of cookie dough into a baking sheet. Bake for 10 minutes.

Remove from the oven and allow to cool for a few minutes. You want them still warm, but cool enough to handle, and they don't fall apart.

Match up cookies by size, placing 1/2 of the cookies face down on a cooling rack. Top with a peanut butter up, and the matching cookie. The heat from the cookie will melt the peanut butter cup. If they get too melty you can put them in the fridge to harden quicker.

Cool completely before serving.