In Japan, kabocha squash are in season from summer to fall, but in North America and Europe fall (autumn) is the big winter squash season. Frozen kabocha squash is a great freezer stock item for bento making, and it’s very cheap and ubiquitous in Japan. Since it’s not so ubiquitous where I live, I try to freeze some of my own around this time of year, when fresh ones are abundant and inexpensive.
The type of squash I usually use is the bright orange colored one sold as red kuri squash, hokkaido squash, and so on, since it’s the one that is most widely available here. (Kuri is Japanese for chestnut - I’m not sure if the name refers to the shape or the flavor. Hokkaido is the northernmost main island of Japan, where a lot of squash are grown.) Here in Switzerland it’s called Knirps. See more about different kinds of winter squash here . The standard kabocha squash is about 10 inches / 25 cm or so in diameter and a dark green; a well known variety is delica. In any case, make sure you have the right type of squash - it should have a dense, sweet flesh. Pumpkin is too watery and stringy for most Japanese kabocha dishes.
Cut the squash up into chunks. Optionally, randomly peel the skin (hack off pieces of the skin with a vegetable peeler or knife) so that the squash will cook a bit faster. (I find that kuri squash skin is thin enough that I don’t need to do this.) Put into a large pot with enough water to completly cover the cut up squash pieces. Bring to a boil, and then lower the heat and simmer for a few minutes until you can just about poke a chopstick or skewer through a piece. In other words, it should be cooked through but still firm and not mushy.
Drain, then spread out onto a baking sheet or other large, flat surface to cool. Once cooled, divide into single-use portions, wrap each in cling film/plastic wrap, and then put the bundles into a freezer bag or box. Try to use up plain frozen kabocha squash within 3 months.
Frozen kabocha squash is very handy for making brownish-orange colored rice .
This is a classic Japanese ‘Mom’s cooking’ dish, that cooks up in no time with frozen kabocha. It’s a very popular bento side dish; the sweet-salty flavor is a nice contrast to meat or fish. I’ve simplified the ingredient quantities to make the recipe easy to remember.
Put all the ingredients into a pan and bring up to a boil. Lower the heat and simmer, turning the kabocha pieces from time to time, until the liquid has reduced to half - about 15 minutes. Leave to cool in the liquid - the kabocha will absorb flavor from it as it cools. Drain off lightly to pack into a bento box. This will keep in the refrigerator for 3-4 days.
If you are making this from fresh uncooked squash, increase the water by 1/4 cup and simmer a bit longer.
You can freeze the simmered squash itself, in single portions. Put 1 or 2 pieces each into cupcake liners, and freeze them lined up on a tray. Once frozen, the single portions can be packed into a freezer bag. Defrost the single portions in the microwave on the HIGH setting for a couple of minutes, and cool off before packing into a bento box.