Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.

In a large mixing bowl, combine the peanut butter, brown sugar, and granulated sugar. Beat with an electric mixer on medium speed until light and fluffy, about 2-3 minutes.

Add the egg and vanilla extract to the peanut butter mixture, beating until fully incorporated and smooth.

Mix in the baking soda and salt until evenly distributed throughout the dough.

Roll the dough into 1.5-inch balls (about 2 tablespoons each) and place them 2 inches apart on the prepared baking sheets.

Use a fork to create the classic criss-cross pattern on top of each cookie, pressing down gently to flatten slightly. Dip the fork in sugar if it sticks to the dough.

Sprinkle each cookie with a pinch of flaky sea salt before baking.

Bake for 10-12 minutes, until the edges are lightly golden but the centers still look slightly underdone.

Let the cookies cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.