This week I was cooking my favorite meat soup when accidentally my Starbucks Milk Chocolate Latte tipped into the pot. At first it was just a little drip, but I lost the handle on the cup and eventually the whole thing fell in. Now, I once learnt some laws of bittul, and of course you need the dish to have 60 times what fell in to nullify it. But I also distinctly remember another law, "Batla miktzasa batla kulah" - "if some of it was nullified, the whole thing was nullified." Once the initial drops were nullified shouldn't the whole cup be?
You only quoted part of the rule - the full text is (Gittin 33a)
עדות שבטלה מקצתה בטלה כולה
Eidos which are partially nullified are completely nullified.
As R' Hirsch explains, Eidos are the laws that are symbolic of some eternal truth. The prohibition of milk and meat, however, is from the Chukim, those laws which defy human understanding. Therefore, the law of partial nullification does not apply.
It depends what you mean by "milk chocolate latte". There are various opinions.
"Latte" is steamed milk. The amount of foam created by the steaming is too minute to worry that this overpowers the pot of meat to give it any taste, as it is mostly air. Then, I assume that milk chocolate is drizzled on top. Milk chocolate is mainly chocolate to which a small percentage of milk has been added. If they just drizzle a bit of this on the latte foam, again, too little to be concerned about the problem.
If, however the latte is made by melting the milk chocolate into the coffee and then steaming extra milk and putting it on top, there might be a concern that the beverage is primarily milk, and perhaps, the volume of milk may have made your pot milchig.
My bigger concern , here, is not the basar bechalav problem which is assur behana'ah, but the mere fact that you bought Starbuck's coffee which is overpriced and overrated. Perhaps, the Starbuck's coffee is assur behana'ah!