To make English clotted cream in a slow cooker, place 4 cups of heavy cream in the slow cooker on its lowest setting. After 3 hours, remove the slow cooker crock and allow the cream to reach room temperature on a counter, then place the crock into the refrigerator for 12 hours. Skim the cooled layer of cream from the top with a slotted spoon, and stir the resulting clotted cream to create a smooth texture.
To make clotted cream on the range, heat 4 cups of heavy cream over medium heat until it reaches 175 degrees. Use a double boiler and stir frequently to prevent scorching. When the cream reaches 175 degrees, carefully raise the temperature of the cream to 180 to 200 degrees and allow it to cook within the temperature range for 45 to 60 minutes. Then place the top of the double boiler in ice water to immediately stop the cooking process. Cover the clotted cream with plastic wrap, then refrigerate it overnight. The next day, skim the clotted cream from the surface of the liquid using a spoon.
Store clotted cream in a sealed container for up to one week. Use the leftover liquid from creating the clotted cream in recipes that call for whey or as a substitute for milk in recipes for baked goods.