Preheat oven to 350 degrees Fahrenheit
In the bowl of a stand mixture, cream the shortening. Gradually add both sugars and cream well. Next, add egg, vanilla, and peanut butter. Combine well.
In a medium bowl, sift baking soda, salt, and flour together. Add to creamed mixture.
Add Reese's Pieces. Start with half of the box and continue to add based on your judgement.
Roll dough into 4 large balls.
To stuff the cookies, press the center of the dough balls with your thumb so you can put two, stacked Reese's inside. Then, form a ball again to cover the exposed Reese's cups. Make sure you create the dough balls in your hand and flatten the bottom when you place them on the cookie sheet.
Once all dough balls are stuffed, place in the oven for 18-20 minutes. Cut one cookie in half to make sure they are fully cooked.
Serve warm and enjoy!