Very nice image, definately meets the challenge, your focus is fantastic on this image.
The only thing I see that probably hurt you is the shadow and glare both going on in the same area just above the handle of the mug. It distracts from the entire image although it would also be hard to correct.
I like how the photo captues the moment of mixing of the milk and coffee. I wish you had turned the cup so as not to include the handle in the composition. otherwise I like the composition
Tea, not coffee? Or just a fairly light brew of cofee?
I think w/o the bubbles would have been more interesting as more of the swirl could have been seen then. I like the framing of the shot, and the border is thankfully very inobtrusive.