Again, this tastes JUST LIKE what Baker's Bakery in Parma uses on their Date Nut Cake. It's not my favorite, but my wife loves it...I love my wife...therefore...
Put the butter, shortening, sugar, salt and vanilla extract in the mixer bowl of your mixer. I use the whisk attachment on my Kitchenaid because we're going to fluff this up. Turn the mixer on low until everything comes together. Yes, it is thick right now. Turn the mixer to medium and add the water one tablespoon at a time until you have 3 Tablespoons added. Turn the mixer up to high to make the frosting light and fluffy. If it is still too thick, add another Tablespoon of water.
This recipe makes enough to frost one layer. If you double the cake recipe, double this recipe also.
If you use "normal" brown vanilla extract, this frosting will not be white, but more of an off-white, or ecru (yes, that's a color). You can get clear vanilla extract, but I don't worry about it. I care what the cake tastes like more than what it looks like. I'm a guy.