I'd probably make a poppy seed pound cake and just seep the milk or buttermilk with some looseleaf earl grey.
warm it slightly and let it sit for an hour or so before straining the tea leaves out.

I dunno why poppy seed seems like the appropriate cake, perhaps from the picture.

Not exactly a cake, but here's a recipe for Earl Grey brownies that won a contest in Boston: http://www.boston.com/ae/food/articles/2007/10/17/earl_grey_brownies/

There's a recipe for Chai tea cupcakes in Vegan Cupcakes Take Over the World, and there's an Earl Grey variation. To make a cake, just double the recipe. :)

My daughter makes a wonderful Earl Grey cheesecake...http://fareisfair.blogspot.com/2009/04/tea-and-cake.html

Here are two earl grey recipes from the "food blog" search engine. The muffins can easily be converted to a cake with a little more sugar.

http://justbento.com/handbook/johbisai/earl-grey-tea-muffins

and earl grey cupcakes

http://www.notquitenigella.com/2008/06/30/earl-grey-cupcakes/

will this help?

Along the lines of the brownies, I've made Earl Grey truffles that were amazing: the secret ingredient is 4-8 drops of bergamot essential oil in the ganache. (Technically it's not foodsafe, but a few drops is fine. It's not poison.) I would imagine you could add a few drops of oil to any cake or cookie recipe. I've made tea-steeped recipes as well but they just don't have the same punch.

Earl Grey and chocolate are a fabulous combo. My former boss used to have me over to her house and make me earl grey tea with shaved chocolate. The flavors are divine.

Although not really a birthday cake, fruit cake made with earl grey tea is really lovely.

love!

<A HREF="http://www.doriegreenspan.com/">Dorie Greenspan</A> has a recipe in her book <A HREF="http://www.amazon.com/Paris-Sweets-Great-Desserts-Pastry/dp/0767906810">Paris Sweets</A> for Earl Grey Madeleines (from Mariage Frères, the amazing tea company, no less). It has you infuse the butter with the tea leaves and straining them out. I bet you could adapt that technique for any cake recipe that requires you to use melted butter (buttercake or quickbread) or oil (like a chiffon cake).

BTW, Paris Sweets is the same book that the recipe for Korovas/World Peace Cookies first appears and it's got a lot of goodies in there.

I used to work at a European pastry shop that made earl grey madeleines with Earl Grey White Tip loose leaf tea. I replicated it (somewhat) at home by just dumping a bag or two of earl grey tea into the batter. Tea leaves are definitely edible and the kind that come in a bag are already finely chopped. As they bake, the earl grey/bergamot flavor steeps into the little cakes.

I assume that you could easily do the same with a simple white, yellow, or pound cake.

A lot of earl grey teas also add other citrus oils (like orange oil) instead of or in addition to bergamot, so a drop or two of orange or lemon oil to the batter probably wouldn't hurt the aromatics quotient, either!

Good luck!

All of the cakes mentioned sound delicious. One thing I make frequently is a pot de creme where the milk has earl grey steeped in it... it's pretty tasty. http://chubbyhubby.net/blog/?p=564#more-564. Also, it's surprisingly simple.