In a small mixing bowl, whisk together the gluten free flour, baking powder, baking soda, and salt until well combined.
In the bowl of a stand mixer fitted with the paddle attachment, add the softened butter, sour cream, granulated sugar, and brown sugar. Beat on medium speed until the mixture is light, creamy, and fluffy—about 2 minutes.
Add the room temperature egg and beat for another 2 minutes, scraping down the sides of the bowl as needed.
Add the creamy peanut butter and vanilla extract. Mix on low speed until fully combined and smooth.
Add the dry ingredient mixture to the wet ingredients. Mix on medium-low speed until just combined—don’t overmix.
Turn the mixer to low speed and gently fold in the semisweet chocolate chips and chopped roasted peanuts until evenly distributed.
Cover the bowl with plastic wrap or transfer dough to an airtight container. Chill in the refrigerator for at least 1 hour (and up to overnight).
After chilling, preheat your oven to 350°F (175°C). Line a large baking sheet with parchment paper. Using a 3 tablespoon cookie scoop (or a 2 tablespoon scoop for smaller cookies), portion the dough into balls. Roll each portion gently between your palms to create a smoother cookie dough ball if desired.
Optional: Slightly flatten the dough balls before baking if you prefer cookies that spread a bit more.
Place 6 dough balls spaced evenly on the prepared baking sheet (they will spread). Bake in the center of the oven for about 14 minutes, or until the edges are lightly golden brown and the centers look slightly underbaked—they will firm up as they cool.
Allow cookies to cool on the cookie sheet for 5–10 minutes before transferring them to a wire rack to cool completely.
Store cooled cookies in an airtight container at room temperature for up to 1 week, or freeze for longer storage.