Preheat the oven to 350°F (175°C). Grease a 9x5-inch loaf pan and line the inside with a parchment paper sling for easy removal.
In a medium bowl, whisk together the all-purpose flour, baking soda, ground ginger, ground cinnamon, ground cloves, and salt.
In a separate large bowl, whisk the melted unsalted butter, packed dark brown sugar, and unsulfured molasses until smooth. Whisk in the egg until fully combined.
Pour half of the dry flour mixture into the wet ingredients, stirring gently with a spatula until just combined.
Carefully whisk in the hot water. Once absorbed, fold in the remaining dry ingredients and mix just until no dry flour streaks remain. Do not overmix.
Pour the batter into the prepared loaf pan. Bake for 45-55 minutes, or until a toothpick inserted into the very center comes out clean.
Let the bread cool completely in the pan before lifting it out using the parchment paper sling.
To make the glaze: In a small bowl, whisk together the powdered sugar, vanilla extract, and enough milk (1-2 tablespoons) to create a thick, pourable consistency.
Drizzle the vanilla glaze generously over the cooled gingerbread loaf. Let the glaze set before slicing and serving.