This Oatmeal Cookie in a Mug is a quick and easy dessert that can be made in just a few minutes. It's a single-serving cookie that is perfect for satisfying your sweet tooth. The cookie is made with oats, brown sugar, butter, and a touch of cinnamon for warmth. Simply mix the ingredients in a mug, microwave for a minute or two, and enjoy a warm and delicious oatmeal cookie without the need for an oven.