In the bowl of your stand mixer combine room temperature butter, both sugars, and salt and beat at medium speed for 6-8 minutes until fluffy and pale. Halfway through, pause to scrape the bowl and beater with a flexible spatula.

In the meantime combine gluten-free flour, cornstarch, oat flour, baking soda, and cinnamon in a separate bowl.

Measure out your gluten free oats and add-ins and set them aside in a separate bowl.

With the mixer running on low, add the egg, letting it fully incorporate. Pause your mixer to scrape down the sides.

With the mixer on low, slowly add flour mixture to the butter mixture. Mix until just combined.

Add your gluten free old fashioned oats and add-ins at a low speed and mix to combine.

Transfer the batter to a Tupperware container and let the dough rest for at least 4hrs in your fridge - better even if you can let it sit for 12hrs or longer.

Once your cookie dough has rested, allow for it to come to room temperature or until it is scoopable. Use a 2 Tablespoon Cookie Scoop and portion the cookie dough.

Preheat your oven to 350F and line a sheet tray with parchment paper.

Arrange 6 cookie dough balls on a baking sheet, leaving some room for spreading.

Bake Cookies for 10 minutes and rotate your baking sheet.

Bake 6-8 minutes or until lightly golden and beginning to set.

Remove from the oven, and if desired, use a round cookie cutter slightly larger than the cookie to scoot them into a perfectly round shape.

Sprinkle with flaky sea salt.

Allow the cookies to cool for 5-10 minutes on the baking pan before moving to a cooling rack.