Korean fermented soybean paste, called doenjang (된장), is more than just a seasoning or an essential ingredient in many iconic Korean dishes. It's impossible for us to imagine life without doenjang.
Full doenjang recipe: http://www.maangchi.com/recipe/doenjang

Salty, earthy, hearty, incredibly savory and delicious, it adds flavor to many dishes and makes them distinctively Korean. Making doenjang at home takes a long time, you have to be ready to commit to it for one year! It's not hard to make, but takes patience and some hard work, and some special equipment. But as a bonus, Korean soup soy sauce (guk-ganjang:국간장) is a byproduct of making doenjang, so you get that delicious soy sauce for free!

Full guk-ganjang recipe: http://www.maangchi.com/recipe/guk-ganjang

This recipe and plenty more in my cookbook: http://www.maangchi.com/real