Preparation Steps

• To the bowl of a stand mixer fitted with the paddle attachment (or large bowl and electric hand mixer), cream together the egg, brown sugar, peanut butter, softened butter, and vanilla extract on medium-high speed until light and fluffy, about 5 minutes.
• Stop, scrape down the sides of the bowl, and add the flour, baking soda, and optional salt. Mix on low speed until just incorporated, about 1 minute; do not overmix.
• Add the Reese’s Pieces and chocolate chips and blend until just incorporated.
• Using a medium 2-inch cookie scoop, form heaping two-tablespoon mounds. Place mounds on a large plate, flatten mounds slightly with your palm, cover with plastic wrap, and refrigerate for at least 2 hours, or up to 5 days, before baking. Do not bake with warm dough because cookies will spread and bake thinner and flatter.
• Preheat oven to 350F (175C). Line a baking sheet with a Silpat or spray with cooking spray. Place mounds on baking sheet, spaced at least 2 inches apart (bake 8 cookies per sheet).
• Bake for 8 to 9 minutes, or until edges have set and tops are just beginning to set, even if slightly undercooked, pale and glossy in the center. Do not bake longer than 10 minutes because cookies will firm up as they cool.
• Allow cookies to cool on the baking sheet for 5 minutes before removing and transferring to a rack to finish cooling.