In this particular case, I'd probably tackle it with lots of cold coffee, a big roll of paper towels, and a very big box of those cookies. Couple that with some real patience, a partner or long cable release, very fast shutter speeds (given it is outdoors, it'll be the shutter that freezes the moment), and several exposures in sequence.
Putting those ingredients together, I would set up the cup and cookies as needed. Position the camera back a bit, on a tripod and focus. Drop the cookie and then hold down the shutter button on the cable release letting the camera take several shots in sequence. Ideally you'd have a camera that can do 6 or more frames a second, the more the better.
If you didn't get the shot you wanted, clean up, refill the cup, and repeat the sequence. Messy, but also fun. From there you can have a bunch of variants on the theme, such as berries into milk, milk drops into coffee, etc. I love splash photography, myself, it's fun to do.
Now, you could use laser or sound triggers, which takes a bit more setup (and cost), but probably gives you a better chance of getting a shot. I don't find that as much fun, oddly enough, I kind of prefer to have my finger on the shutter and be a part of that process.