In a medium bowl, whisk together the flour, baking soda, and salt until well combined. Set aside.

In a large mixing bowl, using either a hand mixer or a stand mixer fitted with the paddle attachment, beat the softened butter on high speed for 1 minute until smooth and creamy. Reduce to medium-high speed and add the brown sugar and 1/4 cup (50g) of granulated sugar. Beat for about 2 minutes, until the mixture is fully creamed and smooth.

Add the egg and beat for another 1 minute, or until fully incorporated. Scrape down the sides and bottom of the bowl as needed to ensure even mixing. Add the peanut butter and vanilla extract, then beat again until everything is well combined.

With the mixer on low speed, gradually add the dry ingredients to the wet mixture. Mix just until combined—the dough will be soft and creamy. Cover the bowl and refrigerate the dough for at least 1–2 hours, or up to 3 days for best texture and flavor.

When ready to bake, preheat your oven to 350°F (177°C). Line large baking sheets with parchment paper or silicone baking mats.

Prepare the cookie coating by placing the remaining 1/2 cup (100g) of granulated sugar into a small bowl. Remove the chilled dough from the refrigerator and roll it into balls—each ball should be about 1 scant tablespoon (around 18g or 5/8 ounce). Roll each dough ball in the sugar to coat thoroughly.

Place the sugar-coated dough balls onto the prepared baking sheets, spacing them about 2 inches apart. Use a fork to press a criss-cross pattern into the tops of each cookie. Since this flattens them slightly, use your fingers to gently reshape each one into a slightly thicker disc to help prevent over-spreading during baking.

Bake the cookies for 11–12 minutes, or until the edges look set and are just lightly golden. The centers will still appear very soft—this is key to keeping them chewy.

Remove from the oven and let the cookies cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.

These cookies stay fresh when covered and stored at room temperature for up to 1 week.