Step 1

Peel ½ small butternut squash (about 1¼ lb.) and cut flesh into ½" cubes. Peel and finely chop 1 onion. Using the flat side of your chef’s knife, crush 1 garlic clove, then peel and finely chop. Coarsely chop 1 cup kimchi (some kimchi juice is okay; no need to drain).

Step 2

Heat 2 Tbsp. extra-virgin olive oil in a large Dutch oven or other heavy pot over medium-high. Add onion and cook, stirring often, until softened slightly, about 2 minutes. Add garlic and kimchi and cook until kimchi is starting to brown and stick to bottom of pot, about 5 minutes.

Step 3

Add squash to pot and reduce heat to medium. Cover and cook, stirring halfway through, until squash is tender (a paring knife should pierce flesh easily), 6–8 minutes.

Step 4

Remove lid and stir in 1 lb. elbow macaroni, shells, cavatappi, rigatoni, or other short pasta, along with 4 cups vegetable stock or water. If using water, add 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt (if you broth isn't very flavorful, you may want to add a bit of salt too; start with 1/2 tsp. Diamond Crystal or 1/4 tsp. Morton kosher salt). Cover and bring to a simmer; cook until pasta is al dente and most of stock is absorbed (you want some starchy liquid left in pan), 6–8 minutes.

Step 5

Meanwhile, grate 1 lb. sharp cheddar on the large holes of a box grater. Trim and finely slice 4 scallions.

Step 6

Reduce heat to low and add cheese to pot; stir until cheese is melted and gooey, about 2 minutes. Season mac and cheese with a few grinds of freshly ground black pepper and scatter scallions over.