Divide the batter among the muffin cups. (Cupcakes will look about 1/2-full.) Spoon about a tablespoon of the filling into the center of each cupcake.

I bought premade vanilla-flavored iced coffees from Coffee Mate, Dunkin', International Delight, Starbucks, and Cafe Bustelo ...

I tried vanilla syrups from Torani, Monin, DaVinci, and Portland Syrups to find the best one to add to my coffee for extra flavor.