Preheat your oven to 350°F and butter an 8" or 9" square pan (or your favorite ramekins if you prefer individual servings).
In a medium bowl, whisk together the flour, baking soda, ginger, cinnamon, nutmeg, and salt. Set it aside for later.
In a small bowl, mix the molasses, milk, and egg. Set this aside too.
In a mixing bowl, cream the butter and granulated sugar together until smooth. Then, gradually add in the flour mixture and the molasses mixture, alternating between the two, and beat on low speed just until blended. Scrape the bowl’s sides and bottom as needed.
Pour the batter into your prepared pan (or divide it among the ramekins). For the pudding, mix the brown sugar and cornstarch in a separate bowl. Heat the hot water and butter together until the butter melts, then stir this into the brown sugar mixture until combined.
Slowly pour the pudding mixture over the batter in the pan (or scoop it over the ramekins).
Bake for 38-42 minutes, or until a toothpick inserted in the center of the cake comes out clean (don’t poke all the way to the bottom!). Once done, remove from the oven and serve warm.
