FWIW, speaking of kidneys of memory, I had veal kidneys for dinner last night at Chez Denise, an old Paris bastion of Les Halles known for rib-sticking workingman food.
It's been at least 15 years since I had visited this place and oogled them served at an adjacent table: big chunks of rosy kidney in a pungent mustardy sauce that kept wafting over to our table. Chez Denise has always been known and frequently criticized for its gargantuan portions, but I was served about half my ancient neighbor's quantity. And all for the good as they were finely cut up, decently cooked but past my preferred doneness and the sauce was meek, contributing little to the almost flavorless meat, no resemblance to the sinus clearing sauce moutarde of memory.
So they stay on my to-do list. It's funny how difficult it is to find excellent renditions of simple, ancestral dishes.