Preheat the oven to 350 degrees F. Grease a 9 x 13 inch baking pan and set aside.
In a large bowl, cream the butter and sugar until well blended. Add the egg and molasses and blend again. Place the dry ingredients together in a sifter and sift directly into the molasses/butter/sugar mixture and mix. Add the hot water and beat until the batter is smooth. I will be fairly thin.
Pour the batter into the prepared pan and bake for 32 - 35 minutes (mine took exactly 32 minutes), until a toothpick inserted in the center comes out clean. Do not over bake or the cake will be dry.
Serve the gingerbread cake warm or cold with whipped cream sprinkled with cinnamon.