DIY stock to reutilise your scraps when you first think about it seems like a great idea. Those vegetable scraps that you can't (or don't) use like the skin off onions and garlic, peelings from pumpkin, potato, carrot, etc, any ends of herbs. Throw them in a pan, add water and boil until tasty and then strain a few times.
BUT when I reflect I'm not sure if it's as sustainable as it first appears. So I thought I'd share my reflections
Firstly you have to store the scraps - not a huge deal but you don't want them to spoil else they'd have been better off in the worm farm or bokashi bin.
Secondly you have to cook them for a while - which in my house means using electricity. This is important especially if you aren't carbon offsetting your energy supply. Because although you're presumably doing this to help the environment, using electricity often means burning fossil fuels. AND if you do it during peak power consumption...double bad.
Thirdly do you really NEED stock? There are only really a few things that NEED stock and we tend to have whey from cheese making that suits most of those occasions.
Fourthly, time, yep doing this takes time away from other endeavours, would that time be better spent picking the caterpillars off my one week old lettuce seedlings? Probably! There's a LOT of straining happens because let's face it onion scraps and peelings are generally disregarded for a reason.
Finally you still have the waste, those peelings don't disappear, and now them are wet and if you aren't careful they are mixed. The worms don't like onion skins and the bokashi doesn't like things too wet.
For us I don't think this is going to become a habit. I may do it occasionally when there is an immediate full batch of a single thing that I can then put into the worm farm. I'm not going to be buying stock either, I can just add herbs for flavour if I'm desperate
Maybe if you are otherwise sending the scraps to landfill and use a lot of stock it might be more worthwhile, but I'd say change them before making stock production as a priority