For the wet ingredients, using a stand mixer, add butter and brown sugar then mix; add eggs and molasses then mix.
For the dry ingredients, in a bowl, combine flour, ginger, cinnamon, nutmeg, baking soda, cornstarch; mix thoroughly.
Combine the dry ingredients with the wet ingredients in the stand mixer.
Form small, golf-ball sized shapes, and place them into a small muffin pan; pressing with your fingers to form cups (aka bathtubs); bake at 350F for 15 minutes.
Using the other portion of the dough, flatten and roll into an even sheet; press the gingerbread man cookie cutter and carefully place the men on to a baking sheet lined with parchment paper; bake at 350F for 5-6 minutes; after cooling, pipe white icing to form the eyes, mouth, buttons, cufflinks.
For the Bubble Bath Frosting:
In a stand mixer, add cream cheese, powdered sugar, brown sugar, cinnamon, ginger, and eggnog; mix well.
For the assembly:
Pipe little round waves into the gingerbread cups (aka bathtubs).