Sweetbreads in White Gravy

Food in England by Dorothy Hartley, p. 111

Sweetbreads (weight?)
1 slice of bacon cut into lardons
1 stick celery, fine dice
1 bouquet garni
(maybe 1/2 cup milk of cream)
Salt and pepper
Bread slices, well toasted

(referred to http://www.donaldrussell.com/calf-s-sweetbreads-with-mushrooms-in-a-cream-sauce.html)

1. Soak the sweetbreads in cold, heavily salted water for 1 hour. Drain, and rinse.
2. Bring the stock to a boil, season with salt, and add the sweetbreads. Reduce to a simmer and cook 8-10 minutes. Remove the sweetbreads from the poaching liquid and set aside to cool a bit.
3. Meanwhile, cook the bacon very slowly to render the fat and avoid browning the meat. Add the celery and herbs and poach the celery in the fat until it is soft, then sprinkle with flour; cook for another 2-3 minutes to cook off the raw flour flavour. 
4. Drain 3/4 to 1 cup of the poaching liquid from the sweetbreads (and dairy?) into the celery mixture and beat to make a smooth sauce. Season with some salt and pepper. Simmer for about 15 minutes, stirring occasionally, to thicken.
5. Clear any skin, fat or gristle, from the sweetbreads and slice fairly thickly. They should be as white as a piece of bread. 
6.  Place the sweetbreads on top of the celery in the pot. Season to taste with salt and pepper and simmer for an additional 5 minutes to heat through the sweetbreads.
7. Spoon over the dry toast.