I didn't sift my butter cream and now it's gritty. How can I fix it without starting over?

Also is there a good recipe for white chocolate fondant?  Not the plastic but the fondant.

I assume by sifting "buttercream" you mean you didn't sift the powdered (icing) sugar. You could try putting the buttercream through a fine seive, but I really  think you should start over.

Ganache: just substitute white chocolate for the brown chocolate.

"Not the plastic but the fondant" - I don't understand what you are saying. What part of ganache is plastic?

pastrypet,   Sorry I  did mean powder sugar. chocolate plastic is basically white choc. and corn syrup.   you can roll it out to cover cakes.  I was looking for a marshmallow fondant recipe with white choc in it.  I'll be covering a wedding cake .

I never sift my powdered sugar. Just use a paddle attachment and whip it on high. The paddle is meant to press things against the side of the bowl and smooth them out.

Long slow beating should help.  I have a recipe that takes up to 30 minutes and it is the creamiest and I *NEVER!* sift.

Just put it back in the mixer bowl, set it on low and go watch the news or read the paper :)  Check it after 15 minutes.

Kakeladi please share that recipe I've never heard anything like it! 

It is posted in the frosting section of the recipe section:)  It's called "2 of everything".

Sorry I can't give you a link right now.

here it is

http://www.cakecentral.com/recipe/22469/2-icing