Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a medium bowl, whisk together flour, baking soda, and salt.
In a large bowl, beat peanut butter, butter, granulated sugar, and brown sugar until creamy (about 2–3 minutes).
Mix in the egg and vanilla until combined.
Add dry ingredients to wet ingredients and mix on low until just incorporated. Do not overmix.
Roll dough into 1-inch balls. Coat each ball in extra sugar.
Place on the baking sheet 2 inches apart. Use a fork to gently press a criss-cross pattern on each cookie.
Bake for 9–10 minutes, until edges just begin to set. Cookies will look soft and slightly underdone.
Let cool on the baking sheet for at least 5 minutes before transferring to a wire rack.
Notes
Underbake for softness: The cookies should look pale and slightly underdone when removed from the oven. They will continue to set as they cool, creating that perfect soft and chewy texture.
Room temperature ingredients: For the best texture, make sure your butter and egg are at room temperature. Cold butter won’t mix properly, and overly warm butter can cause the cookies to spread too much.
Peanut butter choice: Use creamy peanut butter for smooth, even mixing. Natural peanut butter with separated oil can make the dough too oily and dense.
Storage: Store cooled cookies in an airtight container at room temperature for up to 5 days, or freeze for up to 2 months.
Flavor boost: For a little extra indulgence, sprinkle a pinch of flaky sea salt on top of each cookie right after baking.