This Oatmeal Cream Sandwich Cookie recipe with Sourdough is a classic oatmeal cookie with the added benefits of sourdough, and to make the flavor even more amazing, brown the butter before hand! The brown butter adds a nutty toffee flavor to your cookies. It's just so good! Give it a try! These cookies are both soft and chewy cookies. They make the perfect cookie to pair with filling! I used a butter cream filling for these cookies, but these cookies would also be so good with ice cream sandwiches! Just fill with your favorite creamy ice cream. Vanilla ice cream would be my choice!