This is the recipe I use for kidneys, courtesy of my mum.
"I would try to use Ox kidney", (says my mum), "it isn't always available, then I use lamb kidneys but they have a more mild flavour. I never use pigs kidney, nothing wrong with them it is just I prefer the flavour of the other two.
Ingredients:
500g kidney
1 Chopped onion
Tin chopped tomatoes [I sometimes use two - P]
250g sliced mushrooms
Oxo/stock cube
Mixed herbs
Lea & Perrins worcester sauce
Cornflour
Method:
Fry onion in little oil until soft
Add chopped kidney (remove cores) cook for 5 mins
Add tomatoes, herbs, mushrooms, crumbled oxo and w.sauce.
Leave to simmer [30-40 mins for Ox kidney, 15 mins for Lambs]
To thicken the sauce, mix a heaped teaspoonful cornflour with a little cold water to a thinnish paste and add to saucepan and stir. Should you want the sauce thicker add a little more cornflour.
Serve with boiled rice, few peas and enjoy!"