Season mushrooms and onions
I was taught that I should never season (S P) before cooking mushrooms and onions but to taste after. Is this just a precaution to not over season for does early seasoning negativity effect the end result.
Always season onion before, but salt draws the moisture out of mushrooms, causing them to steam rather than brown.
The reason behind this is probably because both onions and mushrooms leach water as they cook so if you season at the beginning of cooking, those flavors will change by the time the veg is cooked. Then you'll most likely have to season again, which might result in the veg being too salty or spicy from the pepper.
On the other end of the spectrum, some will tell you to season both before and after so that you season in stages of cookery. I am one that goes this method when cooking mirepoix items including onions
There is no never.
Sometimes you do, sometimes you don't.
Depends on what you are making, and the type of shrooms you're using.
For example, if I'm going to stir-fry or even grill shiitake mushrooms, I will season before (and during and even perhaps after) cooking. Buttons, on the otherhand, no way.
So it just sort if depends. Like those undergarments.