Place butter in a medium microwavable mixing bowl. Microwave butter for 30 seconds, or until half melted.
Add sugar, and mix until sugar is fully incorporated in the butter. Add the eggs and whisk until fluffy.
Mix in the orange zest and orange juice. Then mix in the milk.
Add the flour, baking powder, and salt to the bowl. Mix until a smooth batter is formed.
Spray your pie dish with non-stick spray. I use an olive oil spray. Pour the batter in the pie dish. Sprinkle some sugar evenly over the top of the batter to bake a nice sugar-crust on top.
Bake for 20 minutes.
While baking the cake, bring the water, orange juice and sugar to a boil in a Pyrex measuring cup, usually about 1 minute. Stir to make sure the sugar is dissolved, then microwave for an additional minute.
When the cake is done baking, poke holes in the cake with a toothpick and pour the syrup over the surface. The cake will soak it up and add some moisture.