Here is a simple recipe for making your own crema at home. Crema is similar to the French Creme Fraiche and has the flavor of a buttery rich and slightly tart sour cream
Place 1 cup whipping cream in a small saucepan on low and heat just until it is barely warmed. Do not overheat or you crema won't thicken. and 2 tablespoons buttermilk in a glass container. Cover and let stand at room temperature (about 70°F) from 8 to 24 hours, or until very thick. Stir well before covering and refrigerate up to 10 days.