Preheat oven to 350 degrees F (175 degrees C). Grease cookie sheets.
In a large bowl, stir together the flour, sugar, baking powder, salt and mace. Cut in the butter using a pastry blender or rub between your fingers. When butter pieces are no larger than pea size, stir in the egg, vanilla and heavy cream. Blend thoroughly. On a lightly floured surface, roll the dough out to 1/8 inch in thickness. Cut into desired shapes with cookie cutters. Place cookies 1 1/2 inches apart onto cookie sheets.
Bake for 5 to 8 minutes in the preheated oven, until the edges begin to brown. Remove from baking sheets to cool on wire racks. Cool completely before frosting.
To make the frosting: In a medium bowl, beat the confectioners' sugar, 1/2 teaspoon vanilla, 1 1/2 tablespoons of cream and salt until smooth and creamy. Spread on top of cooled cookies. Let the frosting dry before storing or serving.
