Say goodbye to Day 3 reheats.
Lasagna soup
Credit: Getty / ALLEKO

Whether you have a casserole that was an extender for leftovers, or a dish that is a casserole made from scratch, you might often find yourself with leftovers that go beyond just an extra lunch, especially if you only have one or two people living in your house. And even the most delicious casserole is not necessarily something you want to eat for six meals in a row. 

Sure, you can freeze portions of many casseroles for future meals, but what if you could transform the leftovers completely? And for that, may I suggest casserole soup.

How I discovered casserole soup

The idea came to me after dining at a restaurant where the soup of the day was lasagna soup. And while I know that it was simply a spiced tomato soup cooked with broken lasagna noodles, crumbled Italian sausage and topped with cheese, it made me think. Could you turn actual lasagna into soup? 

Lasagna is one of those things that I don't make often, because there are only two of us at home, and as much as we love it, it is a rare indulgence, and always has lots of leftovers. So, I grabbed one of the portions I had frozen from a previous batch, thawed it out, chopped it up, and put it in a pan with some tomato puree and chicken stock. The result? A soup that absolutely tasted like lasagna!

The second casserole to soup experiment came with leftover potato gratin. Looking at the leftovers, just potatoes baked in milk and cream, I realized it was pretty close to a classic vichyssoise. I chopped up some of the gratin, put it in a pan with a combo of milk and chicken stock, cooked until super tender then pureed with my immersion blender to perfect smoothness. 

How to make casserole soup

What I realized in these experiments is that for many casseroles, the only things preventing them from being delicious soups are just a bit of liquid and some seasoning. Even better, with today's increased food prices, if you are cooking on a tight budget, turning leftover casserole into soup doubles the volume while creating a whole new eating experience, which is a wonderful way to keep things affordable.

Here's how to turn your leftover casserole into a delicious soup. 

Start with casseroles that have ingredients you'd usually see in a soup: vegetables, grains, and pasta (that's most casseroles!). Either chop or break up your casserole and put it in a saucepan with an equal amount of liquid. Water works fine for intensely flavored casseroles; stock works for everything. If your casserole was cheesy, creamy, or made with a canned cream-based soup, use milk or a combo of milk and stock to make your soup. Keep your ratio 1:1 by volume; for every cup of casserole use a cup of liquid. This should get you a great soup texture, but if you want it thicker or more stew like, you can reduce the amount of liquid. From there, if it's a creamier texture you're craving, just do a little quick puree and you're done!

Great casseroles to make soup from

Here's some classic casserole-to-soup combos to get you started:

Want to get a little fancier? You can also change the flavor profiles if you get creative. Have a chicken and orzo casserole? Use chicken stock and lemon juice as your liquid, then whisk in beaten eggs once hot for a version of avgolemono. Have a great tomato rice casserole? Add chicken stock, coconut milk, and some ginger or garam masala for a curried tomato rice soup. See you at the stock pot!