Why buy these cultured creams when you can easily make them at home?
Cultured creams like crème fraîche and Mexican crema have many uses. They both begin with heavy cream and a natural culturing agent and end up thick, creamy, and lush. The former is used to dress up fresh fruit, dollop on pureed soups, and even withstand boiling temperatures in a sauce without breaking, while the latter is spiked with lime to garnish countless Mexican and Latin dishes. But both products can be difficult to find, and crème fraîche in particular can be five times the price of ordinary sour cream. Luckily, both are easy to make at home.
For crème fraîche: Stir together 1 cup of pasteurized cream (avoid ultrapasteurized, which has been heated to higher temperatures, killing enzymes and bacteria and even altering the cream’s protein structure, making it hard to achieve the right texture) and 2 tablespoons of buttermilk in a container. Cover and place in a warm location (75 to 80 degrees is ideal; lower temperatures will lengthen fermentation time) until the crème fraîche is thickened but still pourable, 12 to 24 hours. For crema, dissolve 1/8 teaspoon of salt in 2 teaspoons of lime juice and add to finished crème fraîche. Refrigerate for up to two months.