Preheat your oven to 350°F (175°C). Butter and flour a 9-inch square baking pan or line with parchment paper for easier removal. Pro tip: Spraying the pan before placing parchment ensures the paper stays in place while you pour in the batter.
In a medium bowl, whisk together the flour, baking soda, ginger, cinnamon, cloves, nutmeg, and salt.
In a large bowl, beat the butter and brown sugar until light and fluffy, approximately 3-4 minutes.
Beat in the egg until fully incorporated. Stir in the molasses and vanilla extract.
Add one-third of the flour mixture to the butter mixture and stir until just combined. Pour in half the hot water and mix gently. Continue alternating with remaining flour mixture and water, ending with the flour mixture.
Pour the batter into the prepared pan and bake for 45-50 minutes, or until a toothpick inserted into the center comes out clean with just a few moist crumbs. For even baking, rotate the pan halfway through the cooking time.
Allow the cake to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.
If using the lemon glaze, whisk together powdered sugar and lemon juice until smooth, then drizzle over the cooled cake.