Authentic, thick Mexican cream.
1 cup heavy whipping cream (read the ingredients; ideally, cream will be the only one. Carageenan, disodium phosphate or other stabilizers or preservatives can interfere with the thickening action of the cream)
2 Tablespoons buttermilk with active cultures (without the cultures the thickening action won't take place)
1. Gently warm the cream in a small saucepan over low heat, just until it is body temperature! If you have a kitchen instant-read thermometer, it should be about 100°. If you don’t, you can test the temperature by dropping a small drop from the pan onto the inside of your wrist. If you feel cold or hot when it touches your skin, it is not the right temperature. If it’s body temperature, you won’t be able to feel a temperature when it first touches your skin (though it will start to feel cold shortly afterwards as it cools).
2. Turn off the heat and mix in the buttermilk. Pour the mixture into a glass jar and set the lid on top, but don’t tighten it! The live cultures need to breathe to do their thickening thing.
3. Put the jar in a warm spot. A room or outdoors (out of direct sunlight) between 80° and 90° is ideal, but it shouldn’t be over 90°.
4. Let the jar sit for about 12 hours, then tighten the lid and put it in the refrigerator to complete the thickening. After several hours in the fridge, the Crema will be perfectly thick and delicious.
9. Your Crema is ready! Drizzle it over chicken or shrimp tacos, or over enchiladas. It will keep for weeks in the refrigerator.