In a large bowl, mash the banana. (Measure to be sure it’s about ¼ cup.)
Add the melted butter and brown sugar and whisk until evenly combined.
Whisk in the egg yolk and vanilla.
Add the gluten-free flour, baking soda, cinnamon, nutmeg and salt and mix with a rubber spatula until well combined. Stir in the chocolate chips.
Let the dough sit at room temperature for about 15 minutes while the oven preheats. (This allows the gluten-free flour to hydrate.)
Preheat the oven to 350F. Line a baking sheet with parchment paper or a silicone baking mat.
Scoop 2-tablespoon sized balls of dough a few inches apart onto the prepared baking sheet. (I bake 6 cookies at a time.)
Bake for 11-13 minutes until set and golden brown.
Let cool for 5 minutes on the baking sheet, then transfer to a wire rack to continue cooling. Top with flaky salt if desired. Enjoy!
