In the bowl of a stand mixer, or in a large bowl with an electric mixer, beat the butter, sugar, and brown sugar for 2-3 minutes, until light and fluffy.
1 cup unsalted butter, 1/2 cup granulated sugar, 1 cup light brown sugar
Add the eggs and the vanilla and continue to beat for 1-2 minutes, scraping down the sides of the bowl as needed.
2 large eggs, 2 teaspoons vanilla extract
Whisk together the flour, baking soda, cinnamon salt, and oats in a large bowl. Add the dry ingredients and beat on low to incorporate into the dough, then turn the mixer up to high to combine fully. Cover thee dough with plastic wrap and chill in the fridge for one hour, or up to 3 days.
1 2/3 cups all-purpose flour, 1 teaspoon baking soda, 1 teaspoon cinnamon, ½ teaspoon salt, 3 cups old-fashioned rolled oats
Preheat the oven to 350°F and line a large baking sheet with parchment paper.
Use a large (3 Tablespoon) cookie scoop to roll the dough into even-sized balls. Arrange them 3 inches apart on the prepared cookie sheet and bake in the preheated oven for 8-10 minutes, until the edges and top are just set. If the edges spread slightly, swirl a large-rimmed glass or coffee cup around the cookie to reshape it into a circle.
Allow them to cool on the cookie sheet for 5 minutes then transfer to a wire rack to cool completely.
Once they’re cooled, whisk together the powdered sugar, vanilla, and milk in a shallow bowl or dish. Just barely dip the tops of each cookie in the icing, leaving some spots uncovered. Make sure the cookies are cool or they’ll be too soft to dip and could break when you pull them out of the icing. Let the icing set for 15-20 minutes then enjoy.
1 1/2 cups powdered sugar, 1/2 teaspoon vanilla extract, 2 Tablespoons milk
Cookies stay fresh at room temperature for up to 3 days. You can refrigerate the dough for up to 1 week or freeze for up to 3 months. Stack between parchment paper when storing.