There were leftover tortillas in my house last week, quickly going stale. There were tomatillos in the market. For a sometime Texan, this means just one thing: chilaquiles.

OK, let me back up.

Photo of tomatillos.

Tomatillo is a fruit related to tomatoes and cape gooseberries. Photograph by Marisa McClellan

Tomatillos, in case you've never encountered them: Small, round things, pale green and firm, and covered with a papery husk. Somewhat like tomatoes, they are botanically a fruit but get used as a vegetable; they have a sweet, acid tang and make superb green sauce.

Chilaquiles: The best thing you can do with leftover corn tortillas, or one of the best, at least. You fry the tortillas until they are crisp (unless you made chips with them, in which case they are crisp to start with); broil the tomatillos, whizz them in a blender and simmer them; fold the tortillas into the sauce and let them soften; and add chicken, if there is any in the fridge. In my house we eat them for brunch, with a runny egg on top, though not often enough.

I was scraping the last smears of sauce from my bowl when it occurred to me that, though I think of chilaquiles as an odd regional one-off—something that makes Southwestern friends hungry and Yankee ones puzzled—they actually belong to a long tradition: recipes that use old bread, or bread's local equivalent.

Think about it. In Italy, there's pappa al pomodoro, a chunky soup of tomatoes, oil and stale bread. In Lebanon, fattoush, a salad of chopped tomato, cucumber, dry shards of pita, sometimes greens. In Thailand—most of Asia, in fact—there's fried rice, made with previously cooked rice, never fresh; and across the same crescent, there's okayu or congee or jook, rice porridge. In France, pain perdu, what we think of as French toast. In England, bread pudding.

I was sure there were other dishes I was missing, so I asked my friends, who are mostly enthusiastic cooks, or eaters, or both. They added: arancini and bolinhos de arroz, rice fritters from Italy or Brazil. Migas de pan from Spain, almost-inedible bread soaked and fried with seasonings until it breaks into crumbs. Philpy, a Low Country cornbread that incorporates leftover rice. Ochazuke, a  make-at-the-table Japanese soup of rice, green tea and crispy toppings. Even American Thanksgiving stuffing; if the cornbread or wheat bread hasn't staled enough to soak up liquid easily, the stuffing will be sludgy and tough.

Photo of salmon Ochazuke.

Ochazuke—or chazuke—is a Japanese dish that contains green tea and rice. Photograph by Michael Perez

I unroll this long list to make two points: First, these dishes are amazing. (The single best thing I ate during one reporting trip to Thailand—a country where everything is delicious—was a plate of leftover rice fried with crabmeat, chilies and eggs.)

And second, the concept underlying these dishes, no matter where they come from, is the same: The central ingredient is something that would otherwise have been thrown away. Stale bread, hard rice, a tortilla with the texture of a plate—destined for the trash, until a thrifty cook realized that another meal could be made of them.

This is important, because we should all be working hard to put less food in the trash. If we could claw back from the garbage food that gets discarded too early, we could increase the amount of nutrition available for the world's burgeoning population, while honoring the effort of farmers and food processors whose hard work we are about to toss.

When and why food gets discarded is a hot policy issue. Jonathan Bloom estimates in his book American Wasteland that the US throws away almost half of its food. The Environmental Protection Agency quantifies that at 20 pounds of food per person per month: $165 billion worth per year. University of Minnesota researchers wrote in Science a few weeks ago that reducing food waste just in the United States, India and China could feed 400 million additional people.

In various places, there are efforts to reverse this landfill-filling tide. The French discount chain Intermarché is coaxing customers to buy "ugly vegetables"—légumes mochesin a clever marketing campaign. In the United Kingdom, the Best Before Project aims to divert to charities food that is past its shelf-life date but safe to eat. As the New York Times wrote in May, the US food industry—recognizing that most waste occurs not in food production but in buying, cooking and serving—has launched a Food Waste Reduction Alliance.

Of course, figuring out something to do with everything may be the biggest challenge faced daily by chefs, who keep their costs in line by making use of each by-product of a professional kitchen. (Bones and feet? Make stock. Fifty pounds of chard stems? Make pickles.) But looking at my empty chilaquiles bowl, it occurred to me: Home cooks could do this too.

In fact, some home cooks already do, if they are the kind of cook who delights in making something out of nothing. But we don't often celebrate it, even though we're partaking in an honorable tradition. We call it leftovers. We say, "Well, it was on its way out anyway." We apologize.

Let's not apologize.

Saving food from being wasted, while making something delicious out of almost nothing, is an ethical act. It helps the planet, stretches your budget, exercises the muscles of your culinary creativity. I propose we give this long tradition a fancy name—borrowing from French toast, I'd go for la cuisine des perdus, more or less "cooking with discards"—and applaud the ingenuity that reduces waste and gives food a further life. Cuisine des perdus is historic, and global, and tasty. We should all do it more.

This story is part of National Geographic's special eight-month Future of Food series.

If you have a favorite "discards dish," tell us about it in the comments!