Instructions:
- Preheat oven to 350°F (175°C). Line baking sheets with parchment paper. In a medium bowl, whisk together the flour, baking soda, and salt. Set aside.
- In a large bowl, beat the softened butter, peanut butter, granulated sugar, and brown sugar together until light and fluffy (about 2-3 minutes).
- Beat in the egg and vanilla extract until just combined, scraping down the sides of the bowl as needed. Do not overmix.
- Gradually add the dry ingredients to the wet mixture, mixing on low speed until just incorporated. The dough will be quite thick.
- Cover the dough and chill in the refrigerator for at least 30 minutes. This is crucial for preventing excessive spreading.
- Scoop the dough into uniform balls (about 1.5 tablespoons each). Roll gently between your palms to form smooth spheres.
- Place dough balls 2 inches apart on the prepared baking sheets. Using a fork lightly dusted with flour, press down gently on each ball to flatten slightly, then rotate the fork 90 degrees and press again to create the classic criss-cross pattern.
- Bake for 10–12 minutes. The edges should be lightly golden brown, but the centres should still look slightly soft and underdone.
- Let the cookies cool on the baking sheet for 5 minutes before carefully transferring them to a wire rack to cool completely.