Freeze the mini marshmallows in an airtight container for a few hours before baking. This helps keep them from melting too quickly inside the cookies.

Preheat the oven to 350°F and line a baking sheet with parchment paper for even baking and easy cleanup.

In a medium bowl, whisk together the gluten-free flour, baking soda, and sea salt until evenly combined.

In a large bowl, beat the softened butter, granulated sugar, and brown sugar for 2–3 minutes until light and fluffy.

Mix in the peanut butter, then add the egg and vanilla extract. Continue mixing until smooth and fully combined.

Slowly add the dry ingredients to the wet mixture and stir until a soft dough forms. If the dough feels too sticky, chill it for 10–15 minutes.

Gently fold the frozen marshmallows into the dough. Some marshmallows showing through the dough is perfectly fine.

Scoop the dough into balls about 2–3 tablespoons each and place them 1–2 inches apart on the baking sheet.

Bake for 10–11 minutes until the edges are lightly golden and the centers still look slightly soft. Avoid overbaking to keep the cookies chewy.

Let the cookies cool on the baking sheet for 10 minutes before transferring them to a wire rack. Serve slightly warm for the best gooey texture.