Mix together brown sugar and butter until light and creamy. Mix in eggs, pumpkin and vanilla.
In separate bowl, whisk together flour, baking powder, salt, allspice, cinnamon, ginger, nutmeg and cloves. Gradually add dry mixture to wet mixture until fully incorporated. Spread in baking dish evenly. Bake for 20 minutes. Let cool.
Beat cream and butter together until well blended. Add remaining ingredients. Beat until creamy. Spread over cooled cookie bar. Cut into individual bars. Store in refrigerator.