Preheat oven to 350 degrees. Line two baking sheets with parchment paper or baking mats; set aside.
In a stand up mixer, cream together the butter and sugar until fluffy and combined, about two minutes. Add in the peanut butter, vanilla, and eggs, and mix until combined.
Add in the flour, baking soda, and salt, and mix on low speed until just combined. Use a rubber spatula to fold in the chocolate chips and Reese's Pieces.
Scoop out balls of dough and place on a cookie sheet leaving about 2 inches between each cookie. If necessary, add any fallen Reese's Pieces to top of cookie while pressing down lightly on on cookie.
Bake for 10-12 minutes, being careful not to over bake. Cool baking sheet for a couple of minutes then move to cooling rack to cool completely.
Notes
If you don't have a stand mixer, you can use a large bowl and hand mixer for this recipe.
This recipe makes about 4 dozen cookies. The recipe can easily be halved to make just 2 dozen cookies instead.
The dough itself can be a little crumbly because of the peanut butter. If it is, just use your hands to squeeze the cookie batter together when putting them on the cookie sheet.
If any of the chips or Reese's Pieces fall out (which tends to happen with a peanut butter dough), just push them back on top of the cookie before baking.
These cookies don't spread much at all when baking so you can squeeze a lot on the sheet. If you are looking for a flatter cookie, you'll have to flatten them out with your palm before baking.
Also, don't expect these cookies to change much in color when you bake them either. Be sure to stick to the 10-12 minute baking time and check the bottom of the cookie for doneness. Cool on a wire rack.
Leftover cookies can be stored in an airtight container in the refrigerator for a week or freezer for two months.