In a double boiler, mix the molasses, brown sugar, and spices.
Cook over medium heat until the sugars are dissolved.
Remove from heat and stir in the baking soda. Let cool.
In a large bowl, beat the butter until creamy.
Mix in the sugar-spice mixture.
Add the egg.
Mix in the flour, 1 cup (150 g) at a time.
Form 2 disks, wrap in plastic wrap, and refrigerate for at least 1 hour, up to 2 hours.
Roll out the dough, one disk at a time, to 1/4″ (0.5 cm) thickness on a floured surface.
Cut out biscuits using various cookie cutters.
Bake on an ungreased baking sheet in the top of a preheated oven at 350F (180 C) for 12 to 15 minutes.
Remove from the oven and let cool completely before decorating.
Repeat with the remaining dough.
Decorate with royal icing.
Royal icing:
Beat the egg whites with the lemon juice until well combined.
Add the sifted powdered sugar and mix until a smooth and shiny mixture is obtained.