In medium bowl combine flour, baking soda, ginger, cinnamon, salt & nutmeg: set aside.
In electric mixer bowl beat 1/2 cup butter & sugar on medium speed until creamy. Add egg, continue beating until well mixed. Reduce speed to low. Beat, alternately adding flour mixture with molasses & 1 cup water and beating after each addition; just until blended.
Pour batter into 13" x 9" pan: sprinkle with 3/4 cup brown sugar.
In medium bowl combine 1-1/2 cups hot water and 1/3 cup melted butter: carefully pour on top of batter.
Bake 40 - 45 minutes, until cracked on top. Serve warm, with vanilla ice cream or freshly whipped cream.