1. Preheat oven to 350 degrees and line a baking sheet with parchment paper. 2. Add butter, brown sugar, and sugar to a large bowl. Beat until smooth and creamy. 3. Add vanilla and egg and beat to combine. 4. In a separate bowl, whisk together the gluten free baking flower, cornstarch, baking soda, and salt. Add the flour mixture to the sugar mixture and mix until combined. 5. Drop dough by ¼ cupfuls onto the prepared baking sheet. Flatten the cookies slightly and top 6. with a sprinkling of sea salt. 7. Bake for 14 to 16 minutes, until edges are golden brown but centers are still soft. 8. Allow to cool on the baking sheet for 5 minutes, then transfer to a wire cooling rack to cool completely.