Dashi stock

Dashi stock.
Sounds complicated?
It is pretty simple.
There are a few method to get it better, but I will write simplest method here.

2 inch by 1/2 ich kelp
2 litteres of water.
If you like to get more umami, add a few pieces of dried shiitake. 
Boil a piece of Konbu( and shiitake)  from cold water, once it reached boiling, stop heat and leave it for a while.
Konbu will be slimy so take it out when it's cool down.
You can keep it in your freezer or fridge.