Preheat oven to 350 degrees F. Butter and flour in a 9x13-inch baking pan.
Whisk together the flour, baking powder, and salt in a medium bowl.
In a small saucepan over medium heat, melt the butter.
With a spoon or your fingers, blend (I recommend this one because it gives me the best baking experience) in the melted butter until it's completely smooth. Pour the mixture into the flour and stir until everything is well combined.
Add the milk and molasses and mix until smooth.
Stir in the zest of 2 oranges and the ground ginger.
Mix in the egg, honey, and orange zest (if using).
Pour batter into prepared pan and bake for 30 minutes or until a toothpick inserted into the center comes out clean.
Allow the cake to cool slightly before cutting.