Homemade Instant Mushroom Gravy

I'm guessing I'm not the only one who grew up in a household that made frequent use of instant gravy mix.  Instant gravy figured into dinners at least once per week, and even made an appearance at Thanksgiving.  While I'll admit that I was never a fan of the stuff, especially when it arrived at the dinner table by the name of Salsbury steak (overcooked hamburger patties topped with gravy, always served with a side of ridiculously over-peppered frozen peas), it certainly was convenient.
There are absolutely occasions these days when I either don't have a pan of meat drippings close at hand, or don't have the time to infuse stock with flavor then turn it into gravy.  There is something to be said for having quick access to a gravy, because sometimes you just need it to tie a whole meal together with something saucy and delicious.  I've only used dried ingredients in this gravy mix, so that it travels well and can even be used while camping.  The recipe is gluten-free and vegan, which makes it great for entertaining.  What's more, this instant gravy actually tastes fantastic because it is full of richness from porcini mushrooms.

Homemade Instant Mushroom Gravy

1/2 c. dried porcini mushrooms, ground to a powder in a spice grinder  (or dried mushrooms of your choice)
1 Tbsp. onion powder
1/2 tsp. garlic powder
1/4 tsp. dried thyme
1/8 tsp. black pepper
1/8 tsp. powdered sumac (or add a dash of vinegar at the end of cooking)
1/2 tsp. salt
1 Tbsp. cornstarch or arrowroot
1 1/2 c. cold water

1.  Mix all of the dry ingredients together thoroughly.  You can multiply the batch and divide it into individual bags or jars for storage.

2.  To make the gravy, combine the dry mix with the cold water in a small pan.  Whisk the gravy together, and continue to whisk occasionally as you bring it to a low boil over medium heat.  As soon as the gravy boils, it should thicken nicely.  No further cooking is necessary.

3.  Taste the gravy, and adjust the salt if necessary.  Serve immediately.