Maybe one of Rose’s bundt cakes would be yummy—maybe there’s one you’ve been wanting to make (like the one with pears), but they never seem birthday-fancy (for most folks), but would be perfect for your uncle, who likes plain cake? I realize the one with pears isn’t totally plain, but it’s pretty plain, and I hear it’s really good!
Another thought is the Domingo (or another cake of Rose’s that she says doesn’t really need frosting). You could put a stencil shape on it (like a leaf or whatever), powdered sugar the top, and remove the stencil for a nice design. I think this is done in the pic section of TCB with a maple leaf, if I’m not mistaken.
You could also make the plain cake—a single layer or a bundt or whatever—and surround it with orangettes (plain or dipped in chocolate)—they would add color, and they’re so delicious!
If you wanted to go a layer cake with filling only between the layers, you could go vanilla/vanilla, which you really don’t come across much. I mean to make one this June, but I’ll probably end up going with cardamon—I can feel it—even though I’m dying to do vanilla/vanilla, because I never have.
You could also fill with lemon curd and blueberries, a’la the She Loves Me cake—not plain, but not super-rich, either. If you feel like you’ve already lemoned, you could do a different curd and fruit.
I’ll bet your uncle likes strawberry short cake—all the old codgers do (and why not). Maybe make a plain cake and make some mascerated strawberries (and whipped cream, if you want) to serve with it?
Anyway, hope that’s helpful!!