If so you will not find out that "some time around the 1870s" a casserole stopped being a dish of cooked rice moulded into the shape of a casserole cooking pot and then filled with a savoury mixture, say of chicken or sweetbreads" and for no apparent reason, out of the blue, became a dish of meat, vegetable, and stock or other liquid, cooked slowly in the oven in a closed pot, its current sense.