In a medium saucepan over medium-low heat, melt the butter to create browned butter. It will begin to foam, which signals the water in the butter is boiling off. Watch closely at this stage. Tiny brown specs of milk solids will begin to appear at the bottom of the pan. Constantly stir and scrape these off using a spatula so they don't stick. As soon as the butter turns chestnut brown and smells nutty, remove the pan from the heat. (This takes about 6-7 minutes.)

Add the brown sugar and granulated sugar to the warm pan and stir until the sugars are incorporated and smooth. Place the mixture into the refrigerator to chill for 10 minutes.

While the mixture is chilling, preheat the oven to 325°F and line two baking sheets with parchment paper.

After the brown butter mixture has cooled slightly, remove it from the refrigerator. Stir in the eggs and vanilla.

Add the flour, oats, baking soda, salt, and cinnamon. Mix until combined.

Gently fold in the white chocolate chips and semi-sweet chocolate chips.

Using a 2-tablespoon scoop, drop the cookie dough onto the lined cookie sheets, leaving about 2 inches between each cookie. Using your hand or the bottom of a glass, press each cookie down slightly.

Bake for 11-13 minutes, or until the edges just start to turn golden. (Do not overbake.) Remove from oven and let cool for a few minutes before transferring the cookies to a wire rack to continue to cool.