In a small bowl mix the ingredients for the topping. Pre-heat your oven to 375 degrees. Put all the dry ingredients into a mixing bowl and add the molten butter to it. Whisk it well and add an egg, milk and juice to it and whisk it some more after adding the vanilla essence to it. A sturdy whisk will come in handy at this point. Pour the mixture into a 9 inch baking tray that has been greased and pour the topping over it. Pop this into the oven for about 30 minutes, cool it for 5 minutes more and your Orange Coffee Cake is ready.