A food mill is a great way to make mashed potatoes, but it's not the only option. You can also use a ricer, food processor, or even just a fork to get the job done. If you don't have a food mill, a ricer is your next best bet. It will give you similarly smooth and lump-free potatoes. Just make sure to cook your potatoes until they're very soft before putting them through the ricer. A food processor can also work in a pinch. It won't give you quite as smooth results as a ricer or food mill, but it will still be much better than using a fork. Just be sure to pulse the potatoes rather than running the machine continuously, or you'll end up with mashed potato soup. And if all else fails, you can always use a fork. It's not ideal, but it will get the job done. Just be prepared for a bit more work, and some less-than-perfect results.