Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper to prevent sticking.

In a mixing bowl, combine the creamy peanut butter, brown sugar, and granulated sugar. Use an electric mixer on medium speed to blend until smooth and creamy, about 1-2 minutes.

Add the egg and vanilla extract to the mixture. Beat until fully incorporated, ensuring the egg is well mixed in.

In a separate bowl, whisk together the gluten-free flour, baking soda, and salt. Gradually add this dry mixture to the wet ingredients, mixing on low speed until just combined. Do not overmix.

Using a tablespoon or cookie scoop, drop rounded balls of dough onto the prepared baking sheet, spacing them about 2 inches apart.

Press a few mini marshmallows into the center of each cookie dough ball, ensuring they are slightly embedded.

Bake in the preheated oven for 10-12 minutes, or until the edges are lightly golden. The centers may look slightly underbaked, but they will firm up as they cool.

Remove from the oven and let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.