Preheat the oven to 350 degrees Fahrenheit. Line two cookie sheets with parchment paper, or silicone baking mats.
Add the brown sugar and butter to a medium sauce pan, and heat over medium heat, stirring often until the butter is melted, and the mixture is a thick caramel paste. 1 cup brown sugar, 1/2 cup unsalted butter
Remove from the heat and stir in the flour, vanilla, and salt. 2 TBS all purpose flour, 1 tsp vanilla extract, 1/4 tsp salt
Let the mixture sit for 10 minutes to cool.
Add in the egg, and stir it until just combined. 1 large egg
Add in the oats and stir them into the mixture evenly. 1 cup old fashioned oats
Scoop the batter in 2 teaspoon portions onto the prepared baking sheet, leaving about 3 inches between each cookie to allow them to spread.
Spread the batter out into a thin layer using the back of your spoon.
Bake the cookies for 5 to 8 minutes, until the edges of the cookies turn a dark golden brown color.
Let the cookies cool on the cookie sheet for at least 10 minutes, then transfer them to a cooling rack to cool completely.