Out here, in Southern California, you can buy miso at just about any regular grocery store, even Trader Joe’s carries it (and Whole Food, but it’s way more expensive there) but Asian markets, which abound, will always have it, and have lots of different brands, and it’s super cheap. It lasts almost indefinitely, so even if you get a tub of it, which is usually about the size of a tub of margarine, you can use it all year long and it will be fine. You keep it in the fridge.
It’s basically fermented soybean paste. It has a salty, nutty, umami flavor. In addition to being used as a base for miso soup, it’s also used as a flavoring agent for other Asian-style foods.
Here are a few recipes using miso:
Miso Glazed Salmon
Broiled Tofu with Miso Glaze and Asparagus
Mushrooms in Miso Sauce with Udon Noodles
Coconut Curry with Miso Gravy
Vegetarian Miso Ramen with Roasted Sweet Potatoes, Egg, and Sesame Broccolini
Coriander Chicken Thighs with Miso Glazed Root Vegetables
Miso Ginger Salad Dressing
You also might enjoy these Sauces : P