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My family ate a lot of spaghetti when I was growing up. Naturally, there were always containers of leftover pasta in the fridge. Because simply reheating leftover spaghetti in the microwave gets boring, and frying it up is tasty but oily, every once in a while my family turned spaghetti leftovers into a cheesy, crusty baked pasta, or spaghetti pie. Toss with grated Parmesan and mild cheddar for the cheesiness of a mac and cheese, add cooked ground chicken (replacing the beef my family used) to make it super meaty, and bake in the oven for a super crunchy top. Why cheddar? The mild flavor works well with tomato, and the texture turns creamy instead of stringy. Though this dish is ideal (if not better) when made with pasta from the night before, it's easy enough to get on the table in under an hour without using leftovers.
When I set about recreating this dish, my first thought was to streamline it. Boiling pasta in advance seemed like a time killer, so I experimented with a technique of baking raw pasta right in the sauce. For dishes such as lasagna (or my chicken pasta bake) this works great—simply add extra liquid for the pasta to soak up. Not so here. The delicate strands of spaghetti got mushy, and the sauce became too starchy. Even fresh cooked pasta, though less starchy, baked up too soft.
To get the firm strands of spaghetti that I remembered, I thought about why fried rice is so much better when made with leftover rice. The answer is retrogradation. When freshly cooked, the gelatinized starches are hydrated and the gelled structure is soft. When left to sit, the starches begin to set up into a firmer, more crystalized structure that are better able withstand a second cook and still stay firm. Chilling the starch speeds this process up somewhat, so that's what I did. I cooked the spaghetti to al dente, and then placed it in the freezer to harden while I prepared the sauce. Toss it all up, bake to set, slice, and devour.