These fun cookie bars will remind you of the oatmeal creme pies you used to get in your lunchbox. They are super easy to make and will give you a taste of childhood!
Preheat oven to 350°F and grease a 10x15-inch bar pan.
Stir together butter, brown sugar, molasses, and vanilla.
Add eggs and mix well.
In another bowl, stir together dry ingredients.
Add dry ingredients to wet ingredients, stirring until just combined.
Spread in prepared pan and bake for 25-30 minutes or until set.
Allow to cool completely before frosting.
Marshmallow Fluff Buttercream
In mixing bowl, beat butter until light and fluffy.
Add remaining ingredients and mix on medium speed for 4 minutes.
Spread over cooled bars. Decorate with sprinkles if desired.
Cut into squares and enjoy.
Notes
These cookie bars can be stored at room temperature for a couple of days. They are at their chewy best when stored at room temperature.For longer storage, refrigerate in an airtight container for up to a week. Or freeze them for up to three months.If you chill them until the frosting is set, you can stack them for storage. But I would but them in a single layer before you bring them back to room temperature.