Preheat oven to 350 degrees F (177 degrees C). Line a baking pan with parchment paper.
In the bowl of a stand mixer, cream together the softened butter and the brown sugar. Scrape down the bowl.
Add eggs and vanilla. Mix until fully incorporated.
In a large bowl, combine brown rice flour, potato starch, tapioca starch, xanthan gum, baking powder and baking soda. Stir to blend.
With the mixer running on low, incorporate the dry ingredients into butter/sugar mixture.
Add the gluten free oats and chocolate chips, and mix until fully combined.
Using a cookie scoop (or two tablespoons), drop cookies onto the prepared baking sheets, leaving about 2-inches (5 cm) between cookies.
Bake in preheated oven for 11-12 minutes, depending on your oven. You want them to be slightly browned around the outside, but still slightly moist in the middle.
Allow to cool on cookie sheet for 5 minutes before transferring to a wire rack.
Cool completely, then store in an airtight container.
You can also make bakery sized cookies using this recipe. Scoop about 1/4 cup (60 ml) of dough per cookie, and flatten just slightly with the palm of your hand. Leave 2-inches between cookies. You will need to increase your bake time to about 13-15 minutes, depending on your oven.
Recipe by Faithfully Gluten Free at http://www.faithfullyglutenfree.com/2010/09/gluten-free-oatmeal-chocolate-chip-cookies.html