The basic idea is you heat cream until it gets just slightly cooked, cool it until it separates, and scoop off the thick part.
why: To go with scones.
what: 1 pint non-pasteurized heavy whipping cream (at least 5.5 g fat in 15 ml), or add a tablespoon of butter if the only non-pasteurized cream you can find is lighter (mine was 4 g fat in 15 ml).
where: In a 4-cup pyrex, covered with foil, in a 180F oven. Some sites recommended cooking it on the stove to 180F, which is below a simmer, but I tried that and I couldn't get it to not simmer. A double-boiler would probably help with that.
when: Let it heat for as long as possible. I only left it for 6 hours and it was ok, but this site recommends more like 8 or 12 hours.
When you take it out of the oven, there should be a yellow skin on top, and I saw a bit of stratification in the cream below.
Stick it in the fridge, still covered, overnight. In the morning, separate out the different layers. I got four layers, from top to bottom: yellowy dried-out butter (discard), very thick stuff I'm calling clotted cream (white in the picture), runnier but still pretty thick stuff that's probably in the range of whipping cream (creamier-colored with few bubbles), and some bubbly watery stuff on the bottom (discard).