Replacement for onion and garlic

I have a friend with the same problem. He was over this past Sunday for dinner and I made a rhubarb-beef khoresh, a Persian dish. It called for onions, but not garlic. I omitted the onions and used fresh ginger. I had asked whether he could tolerate onion juice and that was a go, so I tossed some in (available bottled in grocery stores). The dish was delicious, even without those tasty onions.

A pinch of asafetida spice. It stinks to high heaven when you sniff the spice jar, but add 1/8th of a tsp (NO MORE) into the oil you use to fry your other ingredients when starting the dish. It 'blooms into a lovely garlicky aroma.

My nan just plain doesn't like onions garlic chives etc..... I find it hard work to cook for her. It can be useful to think outside the box, not necessarily think of a direct replacement (although celery gets added in some things) but of a different flavour... For example a cottage pie without onions had some really good bacon in it- it akes it completely different, but very tasty! Bell peppers are another veg that's ets subbed in sometimes.

That is a tough one. My father has the same issue and it has made cooking a challenge for my mom. As others have mentioned, I guess it would depend on the reason this person can't eat garlic and onions (my Dad's is GERD - so that rules out other allums as well). It would also depend on what type of recipe you are trying to adapt. If you are looking to add flavor that will be lost from omitting the onions and garlic, fresh ginger could add flavor to the right recipe. Obviously. that wouldn't work for marinara sauce, but could in a stir fry or a variety of soups. Good luck.

If this person cannot tolerate onions because of, um, "gas", I've had great success substituting sweet onions (Maui, Wala Wala, Vidalia, etc.) for standard. And as mentioned above, shallots can stand in for either or both.

Wow, that's a really tough one! I have a friend who is allergic to garlic, and she calls it "her cross to bear." I don't think anything can exactly equal the effect of garlic or onion, but I have a few ideas. Some things to try in moderation--asafetida or black salt. These are commonly used in Indian cuisine, and I've been able to find them at Indian grocers. Both are very pungent--asafetida especially--so you only need to use a tiny bit (1/8 to 1/4 tsp depending on how much food you're making), and be sure to store it carefully--it has a tendency to permeate other ingredients (double bag it or place the container inside a glass jar). When you use asafetida, sauté it briefly as you would garlic. Cooking the asafetida is what makes it palatable. As for black salt, it's rather sulfuric, so use in moderation. You don't have to cook black salt to make it palatable--I've used it in raita with success.
One thing you didn't mention is whether the person you're cooking for is allergic to all alliums. If not, try using leeks (a personal favorite), chives, or shallots. Hope this helps!