I have a cake in the oven tonight that you might have to try, considering your grapefruit bounty. I came across the recipe when I was trying to decide whether I wanted to try another batch of marmalade that used pureed fruit instead of chopped.
The original calls for orange, but I'm obviously substituting. There was also an error because it called for confectioner's sugar but should have been caster sugar. (fairly obvious as it also called for icing sugar at the end) I dug around and found this one, which does call for caster sugar. I'm just using regular granulated. You may not have the 1/2 cup marmalade on hand to spare, or want to use it, but with all those grapefruit you should make your own!
I'll let you know how it turns out
http://vitosmum.multiply.com/recipes/item/60
Re: **elkaysmom**
You have my attention
How'd the cake turn out? I was planning on trying out a grapefruit marmalade this week so this would be perfect.