Heat the oven to 350°F. Coat a half-sheet pan with nonstick spray and dust lightly with flour.

In a large mixing bowl, beat the softened butter, brown sugar, and orange zest on medium speed until pale and fluffy, pausing to scrape the sides and bottom of the bowl.

Add the egg and vanilla extract, then beat again until fully blended. Scrape the bowl once more.

In a separate bowl, whisk together the flour, ginger, cinnamon, cloves, nutmeg, baking soda, baking powder, and salt.

In a glass measuring cup or small bowl, stir the warm water, molasses, and maple syrup until combined.

With the mixer running on low, add the dry ingredients and the molasses mixture in three additions, starting and ending with the dry ingredients. Beat briefly after each addition just until combined.

Scrape down the sides of the bowl and use a spatula to fold the batter from the bottom, making sure everything is evenly combined.

Pour the batter into the prepared pan and spread it into an even layer from edge to edge. Bake for 18 to 20 minutes, or until a toothpick inserted in the center comes out clean. The cake is thin, so watch it closely and trust an oven thermometer for accurate temperature.

Let the cake cool completely in the pan on a wire rack before frosting.

For the frosting, combine the salted butter, cream cheese, powdered sugar, vanilla, and milk in a food processor and process until silky smooth. If you are using a hand or stand mixer, soften the cream cheese first and beat everything together. Add extra milk a teaspoon at a time if the frosting seems too thick.

Spread the finished frosting over the cooled cake, slice into bars, and serve.