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All this stuff, and more is generally called ''offal', some people who don't like them call them 'guts' (amongst other things)
Actually very nutritious they should not be cooked as most people do - far too much, overcooked they become brittle and lose a lot of their value.
The British like 'Liver & Onions' or 'Liver & Bacon' (mainly for the bacon, I think)
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Personally I used to love my liver just flour coated and fried on each side for about 2 minutes. Still tender and a little bloody/rare!
Veal liver is the best or lambs liver, but unfortunately also the most expensive.
I stay with ox (beef) liver and I just used to love tongue of beef, lamb, pork normally in a Madeira wine sauce
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Brains were a little bit too fiddly for me to bother much, but they are tasty as well.
http://www.sbs.com.au/food/recipes/crumbed-lambs-brains-horseradish-mayonnaise
All of these things tend to be on the cheaper side and all animals (even humans-more or less) also have them
Multi talented, ever heard of 'Cod Liver oil'? Full of good things......!
http://www.webmd.com/vitamins-supplements/ingredientmono-1040-cod%20liver%20oil.aspx?activeingredientid=1040&
We were given a daily dose of this at school in Scotland along with a small bottle of milk and a dose of orange juice.....FREE OF CHARGE......this was during and just after the World War 2 when things were scarce.
It always amused me that somehow there was always enough milk left over for the teacher's Tea......!
Anyway, nowadays- with a surplus of milk they no longer get free milk at school, and Cod is in very limited supply as well. Orange juice nowadays is no rival for what we used to get free, and you have to buy it yourself!
At the moment I can't eat all these things due to my stomach ulcer and digestive problems but I hope I will be able to again later ...........
So - do yourself and your wallet/purse a favour and get:
Not every day, but more often........
Bonne Appétit!