In a large saucepan over medium-high heat, bring the brown sugar, molasses, and butter to a boil. Remove from the heat and let cool slightly. Dissolve the baking soda in 1/3 cup of water and add it to the molasses mixture. Add the remaining ingredients and stir until well blended. Wrap the dough in plastic wrap and chill for at least 8 hours.
Preheat the oven to 350 degrees. Lightly grease a cookie sheet. Roll out the dough to a 1/8-inch thickness on a floured board or surface. Cut with a gingerbread man shaped cookie cutter. Bake for 12 to 15 minutes or until crisp and golden. Allow the cookies to cool completely before decorating. Makes about 4 dozen cookies depending on size of the cookie cutter.
Combine all of the ingredients in a small bowl and beat with a fork until smooth. Decorate as desired. Allow frosting to dry before stacking cookies. Makes enough to frost about 3.5 dozen small cookies.