Preparation Steps

• Preheat oven to 350°F (175°C). Line baking sheets with parchment paper.
• In a large bowl, cream together the butter, brown sugar, and granulated sugar until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla extract.
• In a separate bowl, whisk together the flour, baking soda, and salt. Gradually add to the wet ingredients, mixing until just combined. Stir in the rolled oats.
• Drop by rounded tablespoons onto the prepared baking sheets. Bake for 10-12 minutes, or until the edges are lightly golden. Let cool on the baking sheets for a few minutes before transferring to a wire rack to cool completely.
• While the cookies are cooling, prepare the filling. In a large bowl, cream together the butter and powdered sugar until light and fluffy. Gradually beat in the milk and vanilla extract until smooth.
• Once the cookies are completely cool, spread a generous amount of filling onto the bottom of one cookie and top with another cookie. Repeat with the remaining cookies and filling.
• Serve immediately or store in an airtight container.