To the mixing bowl of a stand mixer fitted with the paddle attachment or using an electric mixer, combine peanut butter, brown sugar, egg, vanilla, and beat on medium-high speed until well-combined and the sugar is fully incorporated and is mixture is no longer gritty or granular, about 5 minutes, or as long as necessary (7 to 8 minutes).*
Add the baking soda and beat to incorporate, about 1 minute on medium-low speed.
Add the toffee bits and beat to just incorporate; don’t overmix.
Using a medium 2-inch cookie scoop, form heaping mounds of 2 to 3 tablespoon each.
Place mounds on a large plate, cover with plastic wrap, and refrigerate for at least 2 hours, or up to 5 days, before baking. Chilling is mandatory, do not bake with warm dough because cookies will spread and bake thinner and flatter.
Preheat oven to 350F, line a baking sheet with a Silpat or spray with cooking spray. Place mounds on baking sheet, spaced at least 2 inches apart (I bake 8 cookies per sheet).
Bake for 8 to 9 minutes, or until edges are set and tops are barely set, even if slightly underbaked in the center. Cookies firm up as they cool, and baking too long results in cookies that become too crisp and hard. The cookies in the photos were baked for 8 minutes, and have chewy edges with soft centers.
Allow cookies to cool on the baking sheet for 5 to 10 minutes before removing and transferring to a rack to finish cooling.
Notes
*Step 1 note: If beating with a hand mixer rather than a stand mixer, 7 minutes+ may be necessary. Don’t shortcut this step. Stop to scrape down the bowl as necessary. Batter may seem oily; this is okay. Note regarding peanut butter: Although natural peanut butter or homemade peanut butter may work, I recommend using storebought peanut butter like Jif, Skippy, Peter Pan or similar so that cookies bake up thicker and spread less. Using natural or homemade peanut butter tends to result in thinner and flatter cookies that are prone to spreading while baking.Storage: Cookies will keep airtight at room temperature for up to 1 week, or in the freezer for up to 4 months. Alternatively, unbaked cookie dough can be stored in an airtight container in the refrigerator for up to 5 days, or in the freezer for 4 months, so consider baking only as many cookies as desired and save the remaining dough to be baked in the future when desired.