For the Julia Child Mastering the Art of French Cooking, some decades ago, gave a lot in time, money, and effort.

The main dish I tried was her

Boeuf Bourguignon.

It turns out, some long notes on a
version of Child's dish now are at

https://cafedelites.com/beef-bourguignon/

That recipe starts with:

"Tender fall apart chunks of beef simmered"

Right, that's the goal and expected result. Right. No doubt.

Well, I tried: Over and over and over, off and on for 10+ years. Devoted a lot of time, money, and effort. Nope, it was a LOT-LOT-LOT and more than that.

Results: All the same. Disaster. Shouldn't just pour it down a drain since that might create expensive plumbing problems.

Then to study the issue, talked with some chefs, read some Escoffier, talked with a US beef industry group, read some materials on science and chemistry of cooking.

The problem was that first description at the beginning of the notes with the URL above, the

"Tender fall apart chunks of beef simmered"

Didn't get that. That's right on target of what I NEVER got. Instead, always the same, for the beef, got only hard, brittle, dry chunks.

Why? It was one word: "Simmer". Don't do that. Never, never, ever simmer beef or any meat. No way. Don't do that. Put the stew in a 350 F oven for some hours? Never
do that either. Use a pressure cooker? In a sense, a pressure cooker, to get temperature over 212 F boiling, is the worst possible approach.

Instead, the solution is simple, dirt simple, in just a few words: Need an actual, clear, meaningful definition of simmer. To be clear, never let the stew get over, say, 180 F. For food safety, 165+ F is a common recommendation. Collagen melts starting at ~160 F. So, for hours of cooking, 180 F risks being too high.

That is, in simple terms, use a thermometer.

Why???? Well, some food chemistry discussions explain that get meat much over 180 F, the proteins will "unwind" and expel their water, and the meat chunks will shrink and become brittle and dry, something like charcoal, nothing like the claim

"Tender fall apart chunks of beef simmered"

And until I learned about some Food Chemistry 101, have a good definition of simmer and use a thermometer, the charcoal-like chunks are what I always got.

The easy way to regulate the temperature is just to use a pot on the stove top where can keep taking measurements with the thermometer.

In simple terms, what "cooking" beef, or any meat, is all about is melting collagen. With the collagen melted out, what is left are the meat fibers, and they are "always" (as I recall from one of the food chemistry sources) tender. Again, collagen starts to melt at ~160 F. If melt the collagen and are at 165 F for food safety, you are DONE.

There is another point: The mention to use beef stock. Yup, should do that. For this, for better flavor, to follow Escoffier, get meat from relatively old cattle. Tough, old, lean meat will have more collagen, and once melted that is desirable although now can buy collagen as dry sheets in a box at the grocery.

As part of the work I did, looked into getting such meat. Finally some packing house people explained that such meat mostly goes to fast food.

So, define simmer as 180- F and get a thermometer. That's the solution.

Finally there is a third point: For soups and stews, onions, carrots, and celery are a classic combination, a "trilogy".