• Preheat oven to 350F (175C) and line a cookie sheet with parchment paper. Set aside.
• Combine melted, cooled butter and sugars and stir until well-combined.
  1 cup (226 g) unsalted butter, 1 cup (200 g) dark brown sugar, ½ cup (100 g) granulated sugar
• Add egg yolks and vanilla extract and stir well. Set aside.
  2 large egg yolks, 1 ½ teaspoons vanilla extract
• In a separate, medium-sized bowl, whisk together flour, baking soda, baking powder, salt, and cinnamon.
  2 cup (250 g*) all-purpose flour, 1 teaspoon baking soda, 1 teaspoon baking powder, 1 teaspoon salt, ½ teaspoon cinnamon
• Gradually stir dry ingredients into wet until completely combined.
• Now you'll need to prepare your oats. Add old fashioned oats to the basin of a food processor and pulse briefly (7-10 times, don't over-do it or you'll end up with oat flour!)
  2 cups (190 g) old fashioned rolled oats
• Stir your oats into your cookie dough until well incorporated.
• Scoop dough by heaping 2 teaspoon-sized scoops and gently roll between your palms to form a smooth round ball (dough may be crumbly). Place cookie dough at least 2" apart on baking sheet and use your fingers to gently press down on each cookie to lightly flatten.
• Bake on 350F (175C) for 12 minutes.
• Allow cookies to cool completely before covering with icing.

TO MAKE ICING

• Combine powdered sugar, 1 ½ Tablespoons milk, corn syrup, and vanilla extract in a small bowl. Whisk until well-combined, if frosting is too thick, add more milk as needed. The frosting has reached the correct consistency when you lift up the spoon and it drizzles a thin ribbon of icing back into the bowl, that should hold its shape for just a second before dissolving back into the rest of the icing (see my video below for a visual).
  1 ½ cups (190 g) powdered sugar, 1 ½ -2 Tablespoons milk, 1 Tablespoons light corn syrup**, ¼ teaspoon vanilla extract
• To dip cookies, grip cookie by the base and dip just the surface of each cookie into the frosting. Pull straight out and place dipped cookie icing-side-up on a cooling rack to set. It will take several hours at room temperature for the icing to set completely and for the cookies to be stackable.