Begin by chilling a mixing bowl for about 1 hour and preheat your oven to 350°F (175°C). Grease or line baking sheets.

Beat together the room temperature butter and brown sugar until smooth and creamy, about 2-3 minutes. Add molasses, egg, and vanilla, blending thoroughly.

In a separate bowl, whisk together flour, oats, baking soda, ginger, cinnamon, allspice, and salt until well-combined.

Gradually add dry mixture to wet mixture, mixing on low speed. Chill the dough for 1 hour in the refrigerator.

Roll the dough into 1 inch balls and place them 2 inches apart on the prepared sheets.

Bake the cookies for 9-12 minutes until golden edges are set but centers are slightly soft. Cool on baking sheets for 5 minutes before transferring to a wire rack.

Once cooled, prepare the cream filling by beating softened butter, powdered sugar, vanilla, and milk until creamy. Adjust milk for desired consistency.

Spread cream filling between two cookies and gently press together. Repeat with remaining cookies.