Remove the thick stems of the callaloo leaves, chop roughly and put into a large saucepan. Add the chicken stock, onion, beef, black pepper, shallots, thyme, chilli and crab meat. Cover and simmer until meat is tender, about 35 minutes.
Add the okra, and cook for 8 minutes.
Remove the chilli. Puree the soup in a blender or food processor. Reheat, and adjust seasonings.
Callaloo can be known by many different names and depending on where you are, can be different types of leaves. Dasheen bush and bhaaji are other common names. Hard to find in the UK, you might have some luck at Caribbean shops, though spinach is indeed a good substitute.