Birthday Cake & Surplus Frosting

I had a commission this weekend to do a birthday cake for a friend's mother. She turned 60, and my friend and his family threw her a surprise party. This is apparently, the year of 60th birthday cakes. Anyway, I was told cake for 20 or so, the Smitten Kitchen Best Birthday Cake, and mocha frosting. It was also mentioned that she likes lilacs, so I riffed a little on that, but in a modern, elegant, feminine-without-being-girlish kind of way.

Then I found myself with tons of extra mocha frosting. Boo hoo, poor me!
What to do with two cups of spare mocha frosting? (Besides sitting down with a spoon and a Colin Firth movie?) Bake chocolate cupcakes!
Ta da!