she's big on always having one thing on the table you KNOW they will eat, right? And I have tried that but then he only eats that item and nothing else?
Yes, that is one of her main principles, but the big thing that DH and I found was that we had to change our attitude towards the latter part of what you said, that DS would only choose to eat one item and nothing else. And that is where the hard part comes in - you need to allow that. You can not make him eat anything and you can't have that much control. Make sure that there are food choices on the table, which includes something he likes, and allow him to choose to eat that and only that. It will take time but he will learn.
A huge key thing for us in getting DS to that point was in NOT SAYING A WORD. It was one of the hardest parts for DH and I and we would be kicking each other under the table (with the occassional shriek from DS "HEY! You
kicked me!" when we missed

). We kept conversation completely non-food related except for things like 'pass the butter' and DH had to refrain from his typical overexaggerated "OHH wow, this is SO yummy, thanks!"

No commenting. No praise for DS for trying something, no comments on what he did or did not eat, nothing AT ALL.
I would put everything out on the kitchen table - and our table is tiny so it took some shuffling most nights!! - and I tried to include some random things as well that DS had not seen before (ie we are a family of olive haters and I bought some olives to put out on a plate) just so that there were new things for DS to look at and decide if he wanted to choose them or not. He was allowed to reach and take whatever he wanted or not take whatever he wanted and his responsibility was getting it into his mouth. And key to the approach is also in allowing that - if he wanted to lean his face down and eat like a dog I would have said ok. The point is in getting him to put food into his body at this point...in 6 months time work on cutlery skills. Mind you my DS did not try to eat like a dog and I would have been clenching my jaw if he had, but DH and I discussed and agreed ahead of time that however he got the food into his mouth was his own choice and we would not interfere ONE BIT. We made everything his own choice and within his own control. And that was key - and DS learned VERY quickly that something different was going on at dinner and that there was no commenting on his food and he DID honestly start eating - not much mind you, and it is not like our problem is GONE but we made some HUGE steps in a short time (about 2 weeks).
After about 2 weeks of the no commenting, no assisting, no interfering approach, one Sunday my DH shouted out to me if I wanted soft boiled eggs for brunch. And did I want one, or two. DS shouted out that HE wanted one and we both stopped, gobsmacked, and stared at each other. Since about 12 months my DS had refused egg in any form (except hidden like in french toast for instance). We struggled to not remark with shock and DH just said ok. Cooked him an egg, called him to the table and he sat down, dipped a piece of toast in it and said it was good and he liked it, but then only ate that one bite, and finished off his toast. MASSIVE step IMO. He used to refuse to even sit at the table with us when we ate eggs. We had a few instances of things like this and we really felt a lot of load off of us as we were seeing the small improvements.
With modelling good eating habits and good food choices, as well as table manners and cutlery use, in time your DS *will* come to know how to do those things. He will not WANT to be stuffing food in with his fingers when no one else is, kwim? But at the moment, it can't be about manners and cutlery, it needs to be about eating and opening his idea to eating. Does that make sense?
One other thing I struggled with was not that he would choose only the ONE thing at the table, but that he wanted to fill up totally on that one thing. So he would always choose bread and just want 4 slices of it. So we did limit the item that he liked - so I would only put two slices of bread on the table and he and DH had to share them, and when it was gone, there was no more of that, but he could choose other things, or choose to be done. Many nights he chose to be done. We had a small bedtime snack each night but I made sure that it was not substantial and not too close to after dinner, but for us it is sort of a part of our family, kwim? I wanted there to be a snack in there so that on nights when he did not eat it was not like an alternative but no matter what, it was there. A piece of toast, a banana, cup of milk, etc.
It was about October when we started with this, and now 5 months later we are able to alter things a bit. Today I refused to let him leave the lunch table until he tasted his lunch. There were no options - we had chicken risotto and some cut up cold leftover chicken. He was allowed to choose one of those things to eat, but he DID need to eat. And he sat there insisting they were both yucky and he hated them,etc etc despite the fact that I know he likes chicken, and kindergarten claims he has been eating rice all month. And prior to that he had spat out even once grain of rice every single time it had ever been offered. Never once had a grain of rice been swallowed from 6 months old. About a week ago he had to answer some questions for a kg activity and he said his favourite food was rice

but I had still not seen him eat it. So today when I said we were having rice for lunch, he said that was great, he LOVES rice.

But then refused to even TASTE it. So I did force it - there are times when I end up saying something and kick myself because it is against our rules but then I feel the need to stick with it. It ended up with him sobbing at the table, and I told him to go find a quiet place to cry and be upset about it, and that he could stay there as long as he wanted, but that when he came out from there, he was going to taste the rice. (And he KNOWS that tasting means spitting out is okay so I was not asking much). He stayed away for about 5-7 minutes and came back and agreed to try the risotto. He ate a bite, instantly said "MMm, that's yummy mama, thanks!" And then refused to eat any more - because he didn't like it. ARGH. So I did make him sit there until he finished. Because it is definitely a mental thing at that point.
BUT I could not and did not do that at all 5 months ago when we started this approach. It took us nearly half a year to get to that! We do still try to stick to the rules of no commenting, no control, no rules and allow choice as much as possible but I find we do deviate a wee bit now that things have opened up. Sometimes it backfires and we need to go back to the start again. But truly, by taking all of the responsibilities off of me and allowing him full control things happened fast. Obviously by taking responsibility from me I do not mean he orders like it is a restaurant, I am sure you know how I mean

Our meals are family friendly - he may not like chicken but chicken is a family and toddler friendly food that is easy for him to eat and it's not unreasonable to expect him to start trying it so I count that as family friendly iyswim? And our meals always include things he will like - a small serving of bread, a vegetable he likes (corn or peas or cooked carrots he can pick up with his fingers), a plate with some cut-up cheese, maybe some pickles, etc and then our main meal.
Sorry I have rambled on and on (I'm not into the movie DH chose!!!) and nto sure if I have offered anything helpful or not. Am happy to chat through it with you and support you in your journey

Deb in Oz has been a great shoulder and support for me in getting through this struggle and it meant a lot to me and made the world of difference to have someone to talk with about it along the way and am always happy to pass that support on as well. Even if you choose a different approach
