Many thanks for the suggestions and the links.
Devonshire Cream – in a Crockpot
First a warning: this recipe does not meet food safety standards anywhere. This version is based loosely on Episode 8 of The Edwardians - see link in Tallpoppy's post.
Traditionally Devonshire cream is cooked “on the back of the stove” meaning long time and low temperature. An old caution is “if it boils, it spoils.”
Place raw milk, still warm from the cow in a Crockpot with a ceramic liner.
Adding culture is optional. Gently mix in one ounce of Flor Danica prepared culture or 1/8th teaspoon of Flor Danica DVI culture powder per gallon of milk. Do not over-stir.
Allow milk to sit undisturbed for 12 to 24 hours at room temperature. This allows the cream to rise and the bacteria to grow.
Turn the Crockpot to the setting required to maintain a temperature between 175* and 195* F. Cook uncovered. Do NOT stir. Do NOT allow to boil. After many hours, 8 in my only attempt, the cream’s surface will have a wavy texture, and the edges will have a light brown tinge.
Turn off heat. Allow cream and milk to cool thoroughly – several hours or overnight. Do Not cover.
Using a skimmer, gently lift sections of the cream layer off the surface of the milk. Allow any excess milk to drip off before gently sliding the rounds of cream into a stack in a small glass dish.
Chill thoroughly (several hours or overnight). Serve traditionally at your next “Cream Tea” with sliced strawberries and very plain biscuits.
It's reminiscent of dense cheesecake, it is overpoweringly buttery tasting when warm - much smoother chilled.
I think I could get to the same place more easily by straining some creme fraiche or Sahnequark, and cooking it a little in a double boiler.