Preheat the oven to 350°F. Prepare 2 cookie sheets with parchment paper or silicone baking mats.

In a medium bowl, combine old fashioned oats, all-purpose flour, baking soda, kosher salt, and ground cinnamon; whisk together.

In the bowl of a stand mixer, cream unsalted butter, peanut butter, granulated sugar, and light brown sugar together on medium speed for approximately 2 minutes. Scraping the sides of the mixing bowl as needed.

Next, add the egg and vanilla extract. Mix until well combined.

Reduce the mixer speed to low and add the oat/flour mixture. Mix until just combined.

In a small bowl add 3 tablespoons of granulated sugar. Using a medium sized cookie scoop (I used a size #40 cookie scoop - 1.5 tablespoons worth of dough in each scoop), roll dough into a ball, place in bowl of sugar and coat on all sides. Add dough to cookie sheet. Place each dough ball about 2 inches apart.

Bake for 11-12 minutes, until lightly golden brown. Remove from oven. Rap the cookie sheet against the counter several times to help break air pockets, then allow to cool for 5 minutes before moving to a cooling rack.

 Allow to cool completely before serving! Store in an airtight container at room temperature for up to a week. To keep cookies soft and chewy, store with a slice of sandwich bread.