In a medium mixing bowl, add the whole old-fashioned oats, all-purpose flour, baking soda, cinnamon, and salt. Whisk until combined. Set aside.
3 cups whole old-fashioned oats, 1½ cups all-purpose flour, 1 teaspoon baking soda, ½ teaspoon cinnamon, ½ teaspoon sea salt
In a large bowl with a handheld electric mixer, or use a stand mixer with the paddle attachment, cream together the unsalted butter and light brown sugar until light and fluffy; about 3-4 minutes.
1 cup (2 sticks) unsalted butter, 1½ cups packed light brown sugar
Beat in the eggs, one at a time, then add the vanilla extract and beat just until combined.
2 large eggs, 2 teaspoons vanilla extract
Add the dry ingredients into the bowl of wet ingredients, and mix on low speed just until combined and no flour streaks remain in the dough.
Stir in the butterscotch chips until combined.
1 bag (11 oz) butterscotch chips
Use a medium cookie scoop to scoop the cookie dough, and then place them onto a baking sheet or large plate (something that can fit in the fridge). Refrigerate the cookie dough balls for 30 minutes before baking.
Preheat the oven to 350°F. Line a cookie sheet(s) with parchment paper. Place 12 cookie dough balls per cookie sheet.
Bake for 11-14 minutes or until the edges are lightly golden brown and the centers are mostly set but still look slightly "wet".
Remove the cookies from the oven and let them cool on the warm cookie sheet for about 10 minutes (so they can set and continue baking slightly), before removing them to a cooling rack to cool completely. The cookies can be eaten warm or at room temperature.