Preheat oven to 350°F. Line two baking sheets with parchment paper, and set aside.
In a medium saucepan over medium heat, combine butter and brown sugar. Whisk frequently until just combined and thick.
1/2 cup unsalted butter, 1 cup dark brown sugar
Remove pan from heat and add flour, vanilla and salt. Whisk to combine and let cool slightly for about 10 minutes.
2 tablespoons all purpose flour, 1 teaspoon pure vanilla extract, 1/2 teaspoon salt
Add egg and whisk to combine.
1 egg
Add oats and whisk until well combined and all the oats are coated.
1 1/2 cups old fashioned rolled oats
Using a small cookie scoop (1 tablespoon), drop batter onto prepared baking sheets. Use the back of the scoop or a spoon to spread the batter into a thin layer.Note: You want to make sure you leave plenty of room for the cookies to spread while baking, so I never do more than 6 cookies per baking sheet to be on the safe side. You're going to need a fresh sheet of parchment paper each time, so just keep alternating baking sheets until you've used all the batter.
One sheet at a time, bake for 8 minutes or until the edges have just started to turn a golden brown.
Let cool completely on the parchment paper (but you can slide the baked cookies on the paper over to wire racks to cool completely while you reuse the baking sheet for your next batch).
If desired, drizzle with melted dark chocolate and let set completely. Enjoy!
Dark chocolate
Video
Notes
Can be stored in an airtight container for up to a week.