Preheat oven to 350°F. Line a baking sheet with parchment paper.
Add butter to a large, microwave safe mixing bowl and microwave just until melted. While butter is still warm, add granulated sugar. Mix for 2 minutes (by hand or with an electric mixer on medium speed). Set aside and let mixture cool to room temperature.
In a separate bowl, whisk together flour, baking soda, and salt. Set aside.
Once butter/sugar mixture is cool, add brown sugar and peanut butter. Mix 3-5 minutes, until well combined and lumps are gone.
Add egg and vanilla extract. Mix until smooth, about 1 minute.
Add half of the flour mixture to the wet ingredients, then mix (by hand or on low speed) until well combined. Add remaining flour and mix until fully combined.
Stir in peanut butter chips.
Scoop out 2 Tablespoons of dough for each cookie and shape into a ball. Place them on the prepared baking sheet at least 2 inches apart. Use the flat side of a measuring cup to flatten each ball to about 3/4 of an inch high.
Bake 11-14 minutes, just until edges are lightly browned. Let cookies cool on baking sheet for at least 10 minutes before removing so they can firm up, then enjoy! Recipe makes 12-14 cookies.