Preheat oven to 375 degrees Fahrenheit. Lightly spray a cooking sheet with non-stick cooking spray.

Mix the flour and baking soda in a small bowl and set aside.

Mix peanut butter, butter, and brown sugar in a medium bowl with a spoon until smooth.

Add the egg and the vanilla; beat until smooth.

Add the flour mixture and stir until combined.

Roll the dough into 1-inch balls and place on cookie sheet.

Bake 8-10 minutes.

Remove from oven and allow to cool for 10 minutes - then place in refrigerator and allow to cool fully for another 20 minutes.

In a microwave-safe bowl heat chocolate chips and butter for about 1 minutes; just until melted. Allow the mixture to sit for about 30 minutes or until slightly stiff.

Heat the marshmallow cream in a microwave for 10 seconds to soften.

Spread marshmallow on a cookie, chocolate on another and sandwich together.

Store cookies in a covered container in the fridge.