Preheat the oven to 350ºF (175ºC). Line two baking sheets with parchment paper or silicone baking mats. Set aside.

In a medium mixing bowl, combine gluten-free flour blend, baking powder, baking soda, and salt. Whisk to combine. Set aside.

In a large mixing bowl, add the softened butter, peanut butter, brown sugar and granulated sugar.

Cream with an electric mixer for 2-3 minutes, until light and fluffy, scraping down the sides of the bowl with a spatula as needed.

Add the vanilla extract and egg. Mix until smooth.

Gradually add the flour mixture to the butter mixture and stir until just combined and no more streaks of flour remain.

Chill the dough for 30 minutes.

Use a #30 scoop (about 2 tablespoons) to scoop the cookie dough into uniform balls.

Place dough on the prepared baking sheet, leaving 3 inches in between each dough ball. I can usually fit 6 cookies on a baking sheet at a time. Place the remaining dough in the refrigerator while the first batch bakes.

Bake at 350ºF (175ºC) for 10-12 minutes, until the edges are just set.

Remove from the oven and immediately sprinkle with flaky sea salt. Let cool before serving.