Measure and weigh out 3 cups of flour. Gather the spices.
Place sugar, molasses, cinnamon, cloves, ginger and allspice in a 2-3 quart saucepan. Set saucepan over medium heat and bring mixture to a boil, stirring often as it heats. When mixture starts to boil, remove from heat and stir in baking soda. Mixture will fizz up and become very airy. Stir in butter and allow mixture to cool for about 5 minutes.
Dump slightly cooled sugar/molasses mixture into a mixing bowl and stir in lightly beaten egg. Add flour, 1 cup at a time, until mixture forms a not-too-sticky dough. Form dough into two equal sections. Wrap tightly and chill until ready to use, or use right away if you need to. The dough is easier to work with after it's been refrigerated, however, it's manageable without the chill period.
When ready to cut, preheat oven to 325 degrees F. Roll dough into 3/8 to 1/2 inch thick circles and cut out shapes. Bake on a parchment lined cookie sheet for 12-14 minutes or until cookies appear done. The cookies thicken during baking, so keep that in mind when you are rolling out the dough.
When the cookies have cooled, decorate with icing.
Crack an egg white or all three egg whites into a mixing bowl. With a whisk or mixing spoon, add powdered sugar 1/2 cup at a time and stir until smooth. You may use more sugar, you may use less - go by feel. If icing seems too thick, add a small amount of water. When icing has reached desired consistency, add vanilla.
If you have a decorating bag, stand it upright in a tall glass and pour the icing into the bag. Otherwise, you may just spoon icing over the cookies.