I made some of my famous broth, formed 4 small meatballs and dropped that with a squirt of tomato paste and some parsley into a 1pt pyrex jug and filled it up to 1/2 pt with extra strong broth. Covered it with a silicone mat and nuked it @600W for 4 minutes and ... added 1/2 teaspoon of salt.
Luckily I poured the salt into my hand and dropped it in from a height --- because the entire thing welled up with a bubbly vengeance and poured forth over the edges of the jug.
Superheated much? OMG.
Points to make:
- I was very lucky moving it out of the nuke didn't make it erupt.
- I was even more lucky not to stick the salt onto a spoon and stir. To stir this kind of thing, you'd need a long cooking spoon. But that's not the smart way to do it either.
What I should have done is pull it out at 1 minute intervals and stir it, leave it sit for 20-30 sec before zapping it again.
Be safe and eat well.
 The recipe!
Don't use salt or pepper (and other spices) until you're ready to use the result.
Start with a slow cooker or a pressure cooker (because that closes very well). Set on low heat, you want a very slow simmer, if the pressure valve releases steam, it's too hot. Ideally, no steam leaves the vessel.
Add 1 kg+ of oxtail or other big bones (break with a hammer if not cut), 2 table spoon of vinegar (to leach the bones' goodness) and cover the bones with boiling water.
Add those frozen, broken bird bones, gristle, skin and knuckles you carefully have saved in a freezer bag every time you gnawed or otherwise dissected something delicious. Add more boiling water to just cover.
Add veggies --- 1/2 a green celery head, 4-6 carrots, 1 -2 quartered onions and if you have it, some chopped celeriac or, chopped parsley root(for the gardeners amongst you). And a big bayleaf. Add more boiling water to just cover.
Hour 47 1/2:
Now is the time to optionally add things like parsley stalks (not the leaves) or 1/2 a leaf of lovage (beware. It's nice but easily dominates, pervasively so).
Leave it to cool down, now pour the entire thing through a sieve.
Once cooled down:
It should solidify into a jelly. If not, use bags you put into mugs for easier pouring and tying, before you stick 'em into the freezer (minus the mug). For small cubes, use the ice cube tray, or silicone muffin cups. If you have jelly, use a big spoon to carve off pieces, wrap into cling film and freeze.
The fat is good for frying eggs and other stuff in (skim and heat carefully to evaporate the last bits off moisture), or if you don't like fat, for bribing a deserving doggy with suitably small portioned treats.
You broth stash will go well in soups and the smaller pieces in cling film go well in vegetables and sauces.
Plus, it makes your kitchen smell great for 2 days. This makes about 1-2 litres of very strong broth, depending on how many bones and water you've used. Not enough? Well, make another lot! ;-D