Combine brown sugar, molasses and spices in 1 1/2 quart saucepan. Heat to boiling over medium-high heat, stirring constantly. Boil 1 minute, then remove from heat.
Place butter in large mixing bowl, add hot sugar mixture and stir until butter melts. Blend in eggs.
Stir 2 cups flour and the baking soda together. Gradually mix into the butter mixture. Mix in enough additional flour to make dough stiff. Shape dough into ball. Wrap in plastic wrap and refrigerate several hours or overnight.
Cut dough into quarters. Shape one quarter at a time into balls (refrigerate other dough). Use rounded teaspoonful of dough for each ball. Place on ungreased cookie sheets.
Bake in preheated 350 degree oven until light brown, 10-12 minutes. Cool on wire racks. Store in airtight container.