Preheat the oven to 450° F. Put the bones in a roasting pan and roast until well browned, about 30 minutes.
Transfer the bones to a stockpot and add water to cover by 1 inch, then
add the onions, celery, carrots and salt. Bring to a boil, skimming any
scum that rises to the surface, then lower the heat so the liquid is
gently simmering. Simmer for 4 to 5 hours, adding water as needed to
keep the bones mostly covered.
Strain through a fine-mesh sieve into a large bowl and let cool
completely; skim off any fat that has risen to the surface. Transfer to
jars, cover and refrigerate. If storing for more than 4 days, transfer
the cooled broth to plastic freezer storage bags and lay flat in the
freezer. Frozen broth will keep for up to 6 months.
