Make the cookie dough by beating 1 cup softened butter until smooth and creamy.
Add 1 cup dark brown sugar and beat until light and fluffy.
Mix in 1 cup molasses and 1 tablespoon vanilla extract until incorporated.
In a separate bowl, combine 4 cups flour with 1 1/4 teaspoons kosher salt, 1 tablespoon ground ginger, 1 tablespoon ground cinnamon, 3/4 teaspoon ground cloves, and 1/2 teaspoon ground allspice.
Make a well in the dry ingredients and gradually mix into the wet ingredients on low speed until no flour streaks remain, avoiding over mixing.
Divide the dough into three portions, wrap each in plastic wrap and chill for about 2 hours until firm.
Preheat oven to 350°F (175°C). Line baking sheets with parchment paper.
Roll out one portion of chilled dough on a floured surface to about 3/8 inch thickness.
Use powdered-floured gingerbread man cookie cutters to cut out shapes and transfer them to the baking sheets.
Bake cookies for 8 minutes until edges are set but not darkened.
Allow cookies to cool on baking sheets for a few minutes before transferring to a wire rack.
Prepare Royal Icing by mixing meringue powder or egg whites with powdered sugar and warm water, adding gel food coloring if desired.
Alternatively, make Glaze Icing by whisking powdered sugar, milk, corn syrup, vanilla, and salt.
Buttercream Frosting can be prepared separately and tinted with gel food coloring as desired.
Decorate cooled cookies with your choice of icing using piping bags and tips for detailed designs.
