Brown the butter in a medium skillet over medium-low heat until golden brown, about 5-7 minutes. Let cool for 10 minutes.

Mix granulated sugar and light brown sugar in a large bowl. Pour in cooled browned butter and whisk until smooth.

Add mashed banana, egg, and vanilla extract. Mix until just combined.

In another bowl, whisk gluten-free flour, salt, and baking soda. Gradually add to the wet mixture until just combined.

Fold in dark chocolate chips evenly.

Scoop the dough onto a parchment-lined baking sheet and refrigerate for 30 minutes.

Preheat oven to 350°F (175°C).

Bake cookies for 10-12 minutes until edges are golden. They will firm up as they cool.

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