>Jonathan's first birthday is Saturday and I need a cake and frosting.

    I have made my own frosting using either shortening or coconut oil to
replace the butter. I started with a recipe from a conventional cookbook
using butter and milk, substituting shortening and rice milk. The
measurements are not exact and I'm still experimenting with it, but maybe it
will give you an idea of where to start if you decide to make your own.
    Start with 6 tablespoons of shortening and mix it with a little rice
milk. Then add confectioner's sugar a little at a time, alternating with
rice milk and vanilla extract, until the texture and taste are okay. I
usually end up using about 2 cups confectioner's sugar, 3/4 teaspoon of
vanilla and a few tablespoons of rice milk.
    This icing is very sweet. The amount of icing you get will depend on how
much confectioner's sugar you add. The original recipe called for 4 cups
confectioner's sugar, and would probably make a larger amount. I usually
make this for cupcakes rather than cake, and run out before frosting the
last few. Depending how sweet you want the icing, you might need to start
with more than 6 tablespoons of shortening for a 2-layer cake.
   Coconut oil is trickier to work with than shortening and I've only tried
it 2 or 3 times. It has to be at cool room temperature to work with--too
cold and it's waxy, too hot and it melts. I also couldn't add
proportionately as much sugar as to the shortening. Once the icing reaches a
creamy texture, adding more sugar makes it grainy and lumpy.
   I don't know anything about the potassium content of these ingredients.
Good luck!

Jean Bynum
Burlington, NC, USA