Home made spice blends and rubs are far superior than any shop bought because you can ensure they are fresh, to your liking and no unnecessary additions to the mix. This mix is made with dried shiitake which you can buy in most Asian supermarkets but also very easy to dry at home, you could use porcini if you wish to be extravagant but don't dry your standard button mushrooms as they lack umami when dried. There are endless uses for this rub, coat chicken wings before baking in the oven, add as a seasoning to slow cooked pulled pork, sprinkle on cheese on toast, I would even suggest sprinkling onto freshly cooked paste before further tossing in some cream.
Prep time here is dependant on whether you are drying out your own mushrooms and you will need a spice grinder or coffee grinder, a food processor just won't be suitable.
If you re using fresh mushrooms, cut them in half and dry them out in an oven on it's lowest setting for approx. 8 hours until you can feel all the moisture is gone or if you are lucky to have a dehydrator use that, they will take 8-12 hours depending on the temperature.
In a spice blender/nutribullet/coffee grinder blitz the shitake, salt and chilli flakes to an almost fine consistency then tip into a bowl.
Add all the remaining ingredients and stir through before storing in a jar, this will keep for months in a cupboard, but I doubt very much it will not be used in that time.