Break Up The Oats. Place the oats in the bowl of a food processor (or the jar of a blender) and pulse a few times to break up the oats. Ideally, you want some whole, and some broken up. This just gives the cookie the best texture. Try not to pulverize the oats into flour as this will drastically change the cookie’s texture.
Combine Dry Ingredients. In a medium bowl, combine oats, gluten-free flour, cornstarch, cinnamon, baking powder, baking soda, and salt. Whisk until evenly combined and set aside.
Cream Butter & Sugars. In the bowl of a stand mixer or a large bowl, combine softened butter, brown sugar, and granulated sugar. Cream with the paddle attachment or a handheld electric mixer 2-3 minutes, or until light and fluffy.
Finish Wet Ingredients. Scrape down the sides of the bowl, then mix in eggs, one at a time, followed by the vanilla extract.
Add Dry Ingredients. Scrape down the sides of the bowl again, then add the dry ingredients and mix until ALMOST fully combined, with just a few dry patches left.
Add Mix-Ins. Next, add white chocolate chips and toffee bits and stir on low until just combined and evenly distributed.
Chill The Dough 1 Hour. Cover the bowl and chill in the refrigerator 1 hour. Do NOT skip this step, or your cookies will spread far too much.
Preheat & Prep. During the last 30 minutes of the chill time, preheat the oven to 350 degrees F. and line two baking sheets with parchment paper so you can alternate baking sheets with each batch.
Scoop & Roll Cookie Dough. Use a large cookie scoop to scoop 3-Tablespoon balls of cookie dough. Roll the dough smooth between your hands and place 6 cookie dough balls on a prepared baking sheet.
Bake, Finish & Cool Cookies. Bake 6 cookies at a time in the preheated oven for 10-12 minutes, or until the cookies are slightly golden brown around the edges and the centers look *just* underdone. (They’ll set more as they cool). Remove from the oven and gently shape with a round cookie cutter into perfect circles, if desired. Garnish with a few more chocolate chips and a sprinkle of toffee pieces, if desired. Let the cookies cool 1-2 minutes on the baking sheet before transferring to a wire rack to cool completely.
Repeat this process with remaining cookie dough until all cookies are baked, alternating baking sheets with each batch so you don’t put cold dough on a hot cookie sheet.
Serve & Store. Enjoy once the cookies have cooled. Store in an airtight container at room temperature 2-3 days, or freeze up to 2 months