Grapefruit isn’t for everyone. Luckily, it’s not everyone’s birthday - it is mine though! 
I used this recipe and pretty much stuck exactly to it.
I used three 8" cakes - the recipe also works with four 6".
I was given this mix of sprinkles for Christmas and decided to use them on the top for a little festive touch.
The filling is grapefruit curd and I think this is the first time I have made a curd. Very satisfying to make! There is also fresh grapefruit juice in the cake along with sour cream. With the cream cheese in the frosting, this makes a really nice balance of bitter, sweet, sour, and tangy. The cake is moist and has a very nice tooth.
Apologies for the poor lighting. A combination of time-of-day, time-of-year, and latitude make for difficult conditions for food photography.
ADDENDA: This recipe would work with any fresh citrus you like. It uses 2 cups of fresh juice (one for the curd and one for the cake) and took about 3.5 ruby red grapefruits (the only kind available at the store I usually go to), so whatever you choose, get a lot of 'em!
The original recipe states that the frosting is enough only to frost the cake, not to do special decorating. I had about a cup left over. I wasn’t especially stingy with it, but I also don’t go for especially heavy frosting as that much overwhelms me a bit.
I followed the options for making this over a few days and it worked out really well for me. I wasn’t so exhausted as to resent the cake upon completion. 
And I love grapefruit; so I’ll have to keep this in mind!
