I haven't tried this yet because I need to get to the health food store for a couple of the ingredients, but it sounds like it would be a good substitute for the boxed stuff.  I use the boxed stuff only when I make homemade onion dip (1 pkg soup mix to 1 24 oz carton sour cream).  I have also substituted cottage cheese for the sour cream (when I goof up and think I've got sour cream and it turns out I don't!!)  by putting the cottage cheese into a bowl and using my hand mixer to beat up the cottage cheese until the curds are no longer visible.

The ratio is 5 tbsp of this mixture = 1 pkg onion soup mix (like Lipton).

Can't wait to give it a try!

https://www.spendwithpennies.com/homemade-onion-soup-mix/